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1
Make the Sponge Batter
15 Mins
Room temperature, about 22°C (72°F)
Beat 200g of the softened butter with 200g of the sugar and 5ml of the vanilla until pale and fluffy, about 3 minutes. Beat in the eggs one at a time, then fold in the sifted flour, baking powder and salt, alternating with 100ml of the milk, until just combined. The batter should be thick and smooth.
Stop folding as soon as the flour disappears — overmixing makes a tough sponge.
Done when: The batter is thick, smooth and falls slowly from the spoon.
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2
Marble, Add the Cherries and Bake
40 Mins
180°C (350°F)
Line a 30 x 20 cm tray with baking paper. Spread half the batter in the tray, stir the cocoa into the remaining batter and spread it on top, then swirl the two layers lightly with a fork. Scatter the drained cherries evenly over the surface and press them in gently. Bake at 180°C (350°F) for 30 to 35 minutes until a skewer comes out clean, then cool completely in the tray.
Pressing the cherries in is what makes the wavy marbling as they sink during baking.
Done when: The top is springy, the edges pull slightly from the tray, and a skewer comes out clean.
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3
Cook the Vanilla Custard
15 Mins
Medium heat, about 90°C (195°F)
Whisk the cornstarch into a little of the 250ml milk until smooth, then stir in the rest of the milk, 80g of the sugar and 5ml of the vanilla. Cook over medium heat, stirring constantly, until the custard thickens and bubbles, about 5 minutes. Pour into a bowl, press cling film onto the surface and cool to room temperature.
The cling film on the surface stops a skin forming on the custard.
Done when: The custard is thick enough to coat the spoon and holds a trail when stirred.
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4
Whip the Buttercream and Spread
15 Mins
Room temperature, about 22°C (72°F)
Beat the remaining 125g of softened butter until pale and fluffy, then add the cooled custard one spoonful at a time, beating well after each addition, until the buttercream is smooth and velvety. Spread it evenly over the cold cake, right to the edges, and chill for 30 minutes until firm.
If the buttercream looks curdled, keep beating — it comes back together once the custard is fully mixed in.
Done when: The buttercream is smooth, holds soft peaks and spreads without tearing the sponge.
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5
Glaze with Chocolate Waves
15 Mins
Gentle heat, about 50°C (120°F)
Melt the chopped dark chocolate with the vegetable oil in a bowl over simmering water, stirring until smooth. Pour over the chilled buttercream and spread quickly into a thin, even layer. Before it sets, drag a fork through the chocolate in long wavy lines to make the Danube wave pattern.
Work fast once the chocolate is poured — it starts to set within a minute on the cold buttercream.
Done when: The glaze is thin, glossy and evenly waved, with no bare patches of buttercream showing.
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6
Chill and Cut into Slices
10 Mins
Room temperature, about 22°C (72°F)
Chill the finished cake for at least 30 minutes until the glaze is set, then cut into 12 slices with a hot, dry knife, wiping the blade between cuts so the layers stay clean.
A hot knife cuts the chocolate cleanly instead of cracking it.
Done when: The slices show the marble sponge, cherries, buttercream and glaze in neat layers.
auto_awesome Finishing Touches & Plating
Serve the donauwelle chilled or at cool room temperature, in neat slices, with black coffee — the classic German coffee-table way.
Germany
3h 30m
