Chocolate hazelnut mud cake is an Australian cafe classic, a dense, fudgy slab of dark chocolate bulked out with roasted hazelnuts and finished with glossy ganache. It sits somewhere between cake and brownie, the kind of thing you find under glass domes next to the espresso machine.

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I love this cake because it asks so little of you. One pan for the batter, one for the ganache, and the oven does the rest. The ingredient list is short, the method is nearly impossible to mess up, and the flavor actually improves after a day in the tin. If you have ever paid sixteen dollars for a slice and wondered if you could make it at home, this is your answer.

Why You’ll Love This Recipe

One-pan batter: Everything melts together in a single saucepan. No creaming butter, no folding egg whites, no multiple bowls to wash.
Better the next day: The crumb continues to settle and the flavors meld overnight. This is the rare cake that rewards procrastination.
Crowd-pleasing portion size: One tall cake feeds twelve generously. It looks impressive on a stand and slices cleanly for plating.

The Culinary Secrets Behind This Dish

The long bake at 160 C is what transforms this from a standard chocolate cake into a true mud cake. Low, slow heat gives the butter and chocolate time to set into that characteristic dense, almost truffle-like crumb without drying out. The small amount of self-raising flour provides just enough lift to keep the center from becoming a brick, while the plain flour and cocoa build structure. Cocoa is fat-free compared to melted chocolate, so it deepens the chocolate flavor without adding more fat that would make the cake greasy.

The 20-minute cooling of the melted chocolate mixture before adding eggs is non-negotiable. Hot liquid would scramble the eggs on contact. But there is a second reason: cooling thickens the mixture slightly, which helps suspend the hazelnut pieces evenly through the batter rather than letting them sink. For the ganache, the room-temperature rest is equally deliberate. As the chocolate-cream mixture cools, the cocoa butter crystals reform, shifting it from pourable liquid to spreadable frosting. Rush it in the fridge and you get graininess; let it sit and you get that mirror-smooth finish.

What You’ll Need

Equipment

Deep 20 cm-round cake pan: This tall-sided pan contains the thick batter and allows the cake to rise without overflowing during its long bake. A shallow pan risks a messy oven and dry edges.
Baking paper: Lines base and side so the dense, sticky cake releases cleanly. Without it, you will lose chunks of that precious crust to the pan.
Heavy-based pan: For melting butter, chocolate, sugar, and water evenly without scorching. A thin pan creates hot spots that seize the chocolate.
Whisk: Incorporates the sifted flours and cocoa into the cooled chocolate mixture without over-beating. A wooden spoon would leave lumps; an electric mixer would add too much air.

Ingredients

Cake

Butter, 250 g, chopped: Provides the fat that carries flavor and creates the dense, fudgy texture. Real butter, not spread, for the right richness.
Dark chocolate, 200 g block, chopped: The backbone of flavor. Use a block you would eat straight, not baking chips with added stabilizers.
Caster sugar, 2 cups: Dissolves completely in the hot liquid, contributing moisture and that characteristic crackly mud cake crust.
Hot water, 1 cup: Thins the batter to pour-able consistency and keeps the final cake moist through its long bake.
Plain flour, 1 ½ cups: Builds structure without adding lift. Sifted to avoid flour pockets in the dense batter.
Self-raising flour, ¼ cup: Just enough leavening to prevent the center from becoming completely leaden.
Cocoa powder, ¼ cup: Intensifies chocolate depth without extra fat. Use Dutch-processed for smoother flavor, natural for more bitterness.
Eggs, 2, beaten lightly: Binds the loose batter and sets the crumb during the long, gentle bake.
Roasted hazelnuts, 1 cup, coarsely chopped: Adds crunch and that classic pairing with chocolate. Buy them already roasted or toast raw ones yourself.

Ganache

Dark chocolate, 200 g block, chopped: Melts into the cream for a glossy, rich ganache with serious chocolate presence.
Thickened cream, ½ cup: The fat content lets the ganache set to a spreadable consistency without becoming hard or greasy.

To decorate

Chopped roasted hazelnuts and chocolate curls: Adds texture contrast and signals what is inside. The curls make it look bakery-finished with minimal effort.

Step-by-Step Cooking Guide

1: Prepare the pan and oven

Grease your deep 20 cm-round cake pan thoroughly, then line the base and side with baking paper. Let the paper extend a few centimeters above the rim; this cake bakes tall. Preheat your oven to 160 C, conventional, not fan-forced. The lower temperature is deliberate.

2: Melt the base

Put the chopped butter, 200 g dark chocolate, caster sugar, and hot water into your heavy-based pan. Set over low heat and stir until the chocolate melts completely and the mixture looks like glossy, thin hot chocolate. Remove from the heat and set aside for exactly 20 minutes. It should still feel warm but not hot when you touch the pan base.

3: Build the batter

Whisk in the sifted plain flour, self-raising flour, and cocoa powder until no streaks remain. The batter will be thick and slightly elastic. Add the lightly beaten eggs and whisk again until just combined. Fold in the cup of coarsely chopped roasted hazelnuts. Pour into your prepared pan and smooth the top.

4: Bake and cool

Bake for about 2 hours. The top will crack and the center will feel set but still slightly soft when pressed. A skewer inserted will come out with a few moist crumbs clinging, not wet batter. Cool the cake completely in the pan on a wire rack. It will sink a little as it cools; this is correct.

5: Make the ganache

While the cake cools, make the ganache. Combine the remaining 200 g chopped dark chocolate and thickened cream in a clean pan. Melt over low heat, stirring constantly, until smooth and shiny. Remove from the heat and leave at room temperature until thick enough to hold its shape, about 45-60 minutes. Do not refrigerate unless you are in a hurry, and then watch it like a hawk.

6: Finish and decorate

Turn the cooled cake out of the pan and peel away the baking paper. Invert it onto your serving plate so the flat base becomes the top. Spread the ganache generously, letting it drip slightly down the sides if you like that look. Scatter with extra chopped roasted hazelnuts and chocolate curls. The cake is ready to slice, though it will taste even better tomorrow.

Ingredient Substitutions & Variations

Ingredient	Substitute	Taste & Texture Impact
Butter	Margarine or dairy-free spread	Slightly drier crumb, still good
Thickened cream	Coconut cream	Less smooth ganache, more coconut flavor
Roasted hazelnuts	Walnuts or pecans	Different nut flavor, same crunch

Recipe twists:

Variation	Description & Culinary Details
Espresso mud cake	Dissolve 2 tablespoons of the hot water with strong espresso. The coffee amplifies the chocolate without making the cake taste like mocha. I do this when serving adults after dinner.
Salted caramel swirl	Swirl ½ cup salted caramel sauce through the batter before baking, then drizzle more on top of the ganache. The salt against the sweet is intense and popular.

Allergen Friendly Adjustments

Gluten-Free: Not gluten-free as written. Both plain flour and self-raising flour contain wheat gluten. Substitute a 1:1 gluten-free all-purpose blend plus 1 teaspoon baking powder to replace the self-raising flour. The texture will be slightly more tender but still fudgy.
Dairy-Free: Not dairy-free. Butter and thickened cream are both dairy. For butter, use a good-quality dairy-free spread with at least 70% fat content. For cream, full-fat coconut cream works but will add a faint coconut flavor. I find the ganache less glossy with coconut cream.
Nut-Free: Not nut-free due to hazelnuts throughout. Omit the nuts entirely for a plain chocolate mud cake, or replace with the same weight of chocolate chips for pockets of melted chocolate. The cake loses its signature crunch but stays dense and rich.
Egg-Free: Contains eggs. I have not tested this without eggs. The structure relies on eggs for binding in this dense, low-flour batter. A commercial egg replacer might work but I cannot promise the same fudgy crumb.

Serving and Pairing Suggestions

Espresso: A double shot cuts through the richness and mirrors those roasted hazelnut notes. This is how they serve it in the Melbourne cafes where I first learned to love mud cake.
Vanilla bean ice cream: Cold and creamy against the dense, room-temperature cake. The temperature contrast is the point.
Fresh raspberries: The acidity lifts all that chocolate and stops the slice from feeling heavy on the palate.

Storage, Reheating, and Freezing Guide

Refrigeration: Store in an airtight container at cool room temperature for up to 3 days. The ganache keeps the cake moist. In humid weather, refrigerate and bring to room temperature before serving.
Freezing: The cake freezes well without the ganache. Wrap the cooled cake in two layers of cling film and freeze up to 2 months. Thaw overnight at room temperature, then make fresh ganache to finish. I do not recommend freezing the finished cake; the ganache sweats and loses its gloss.
Reheating: Serve this cake at room temperature or slightly warmed. For a warm slice, microwave individual portions for 15-20 seconds. The ganache will soften to a sauce-like consistency.

Frequently Asked Questions (FAQ)

▶ Why didn’t my cake rise much?

A true mud cake is meant to be dense. The low oven temperature, high liquid content from butter and water, and minimal leavening all suppress rise. The result should be fudgy and flat-topped, not fluffy. If you want light and airy, this is the wrong recipe.

▶ Can I make this ahead?

Yes, and I think it tastes better on day two. The flavors meld and the crumb settles into something even more moist. Store it uncovered at cool room temperature if eating within 24 hours; the ganache forms a protective seal.

▶ How do I know when the ganache is ready to spread?

The ganache needs patience. At room temperature in a cool kitchen, this takes 45-60 minutes. It should hold a soft peak when you lift the spoon. If you refrigerate it, stir every 10 minutes and watch closely; it goes from perfect to solid quickly.

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