Donauwelle — German Danube wave cake

i. Origin & history

Donauwelle is a twentieth-century German bakery cake, and it has no well-documented inventor or birthplace. It became widespread in West Germany in the 1950s and 1960s, the era of the Wirtschaftswunder, when butter, chocolate and jarred cherries became affordable everyday ingredients and home baking flourished. The cake's popularity was helped by German baking-product companies, which printed recipes for it and later sold Donauwelle baking mixes, and by the 1970s it was found in almost every bakery and on many family coffee tables.

The name, 'Danube wave', refers to the look of a cut slice. When cherries are pressed into a layer of chocolate batter on top of vanilla batter, they sink as the cake bakes, dragging the dark batter down with them. In cross-section, the boundary between the two sponges becomes a series of waves. The combed chocolate glaze on top repeats the motif. Since the Danube rises in the Black Forest and flows through southern Germany and Austria, the river was an obvious image.

The cake also goes by another name: Schneewittchenkuchen, or Snow White cake, after the fairy-tale princess with skin as white as snow, lips as red as blood and hair as black as ebony — the white custard, red cherries and dark chocolate. Some families use the two names interchangeably; in other regions, Schneewittchenkuchen is a slightly different version with a whipped-cream topping.

Donauwelle is popular in Austria too, and it is a classic of Kaffee und Kuchen, the afternoon coffee-and-cake ritual. Because it is baked in a tray and cut into squares, it is a favourite for birthdays, school fêtes, church events and office celebrations, where it sits beside Bienenstich and Black Forest gâteau.

ii. How the waves form

Donauwelle is built from a single pound-cake batter, part of which is coloured with cocoa. The plain batter is spread in the tin first and the chocolate batter on top. Then the drained cherries are scattered over the surface and pressed in lightly. As the cake bakes and the batter softens, the heavy cherries sink, pulling streaks of chocolate batter down into the vanilla layer. The result is not a random marble but a series of distinct dips and waves.

For the waves to form, the cherries must be well drained, and the chocolate batter must be thick enough to hold a shape. Wet cherries leak juice into the sponge and leave soggy pockets. If the chocolate batter is too thin, it simply merges into the vanilla, and the cake becomes an even brown.

The topping is German buttercream (Deutsche Buttercreme), made by beating cooled custard into soft butter. It is lighter, less sweet and more stable than a buttercream of butter and icing sugar, but it has one rule: the custard and butter must be at the same room temperature. If the custard is cold, the butter firms into lumps and the cream curdles; if it is warm, the butter melts and the cream turns runny.

The chocolate layer is the last step. A little butter or neutral oil in the melted chocolate keeps it from cracking when cut. It is poured over the chilled buttercream, left to set slightly, and then combed into waves with a cake comb or the tines of a fork.

iii. Ingredients

Makes 16 servings · scroll the side panel to adjust

• 200 g soft unsalted butter (sponge)
• 200 g caster sugar (sponge)
• 4 eggs, room temperature
• 300 g plain flour
• 2 tsp baking powder
• 1 pinch salt
• 5 tbsp milk, divided
• 20 g cocoa powder
• 680 g jar sour cherries (about 350 g drained)
• 500 ml whole milk (custard)
• 80 g caster sugar (custard)
• 40 g cornflour
• 2 egg yolks
• 1 tsp vanilla extract
• 225 g soft unsalted butter (buttercream)
• 150 g dark chocolate
• 30 g unsalted butter or 1 tbsp neutral oil (glaze)

Sour cherries from a jar (Schattenmorellen) are traditional and give the right sharpness against the rich buttercream; drain them well and pat them dry. Fresh or frozen pitted sour cherries also work. Many German bakers use a packet of vanilla pudding powder for the custard; the cornflour, yolk and vanilla custard here is the equivalent. Use soft butter for the buttercream, the same temperature as the custard. A little butter or oil in the chocolate keeps the top layer soft enough to cut cleanly.

iv. Method

1. Make the custard first: heat 400 ml milk with the sugar. Whisk the remaining 100 ml milk with the cornflour, yolks and vanilla, whisk in the hot milk, return to the pan and cook, stirring, until thick and bubbling for 1 minute. Press cling film onto the surface and cool to room temperature (do not refrigerate).
2. Heat the oven to 180 °C (350 °F), conventional heat. Grease and line a 23 × 33 cm baking tin. Drain the cherries thoroughly and pat dry.
3. Beat the butter and sugar until pale and fluffy, about 4 minutes. Beat in the eggs one at a time. Mix the flour, baking powder and salt and fold in with 3 tbsp milk.
4. Spread just over half the batter in the tin. Stir the cocoa and remaining 2 tbsp milk into the rest, and spread it carefully over the vanilla layer.
5. Scatter the cherries evenly over the top and press them in lightly. Bake for 35–40 minutes, until a skewer comes out clean. Cool completely in the tin.
6. Beat the soft butter for 3–4 minutes until pale and creamy. Add the room-temperature custard a spoonful at a time, beating well after each addition, until smooth. Spread evenly over the cake and chill for 1 hour.
7. Melt the chocolate with the butter or oil and cool for a few minutes until barely warm. Pour over the chilled buttercream and spread thinly. When it begins to set, after 5–10 minutes, draw a cake comb or fork across it in waves.
8. Chill for at least 2 hours until firm. Cut into squares with a sharp knife dipped in hot water.

v. Tips & common mistakes

• Keep the custard and butter at the same temperature. This is the most common failure. If the buttercream curdles, warm the bowl briefly over hot water and beat again; if it is runny, chill for 10 minutes and beat again.
• Drain the cherries thoroughly. Wet cherries make soggy patches and stop the sponge from setting around them.
• Spread the chocolate batter carefully. Dollop it over the vanilla layer and spread gently; if you swirl it in, you get a marble cake but no waves.
• Cool the cake completely before adding the buttercream. Any warmth melts the butter, and the topping slides off.
• Pour the chocolate barely warm. Hot chocolate melts the buttercream underneath and the layers blur together.
• Cut with a hot knife. Dipping and wiping the knife between cuts gives clean, sharp layers instead of cracked chocolate.

vi. Variations

Schneewittchenkuchen (Snow White cake) is often the same cake under another name, though some versions top it with whipped cream or a cream-cheese layer. A Donauwelle with pudding cream skips the butter and uses set custard alone, which is lighter but less stable. Some recipes use raspberries, apricots or pears instead of cherries; modern bakeries sell versions with white chocolate tops or a layer of cherry jelly.

The same pairing of chocolate, cherries and cream defines the Black Forest gâteau, and the German love of tray cakes extends to poppy-seed Mohnkuchen and the cheesecake Käsekuchen. For a simpler marbled cake, try a classic marble cake.

vii. Serving & storage

Donauwelle is served cold or cool, cut into squares, with coffee in the afternoon. It needs no accompaniment, though a little whipped cream is sometimes offered. Because it is made in a tray, it is an easy cake to transport and serve to a crowd.

Keep it covered in the refrigerator, where it stays good for up to four days; take it out about 20 minutes before serving so the buttercream softens slightly. It is a good make-ahead cake: it slices more neatly on the second day. Donauwelle also freezes well for up to two months: freeze the squares on a tray until firm, then wrap individually and thaw in the refrigerator.

ix. More from Austrian & German

• Schwarzwälder Kirschtorte — Black Forest gâteau
• Bienenstich — German bee sting cake
• Käsekuchen — German quark cheesecake
• Mohnkuchen — poppy-seed cake
• Prinzregententorte — Bavarian layer cake
• Marble Cake — swirled vanilla-chocolate cake