Donauwelle is a German cake that involves layering two differently colored cake batters, topping them with sour cherries and baking the entire mixture. After cooking, the cake is topped with a layer of buttercream and melted chocolate. The sour cherries are placed on uncooked batter, so they sink during cooking, causing the two colored batters to mix together and create wavelike patterns inside the cake. The resulting donauwelle is a low-rising, rich cake that can occasionally be very dense, depending on the exact ingredients and baking methods. Some recipes call for the addition of ingredients that lighten the batter or keep it moist, like yogurt.
The donauwelle is baked in a sheet pan, unlike some other cakes that use a similar type of batter. The batter itself also lacks the addition of excess moisture, sometimes causing it to be dense and the uncooked dough very tough compared to more liquid batters. The entire recipe, when made in the traditional way, can be quite time consuming with all the different steps that have to be taken and the cooling time required at different points. Alternately, there are recipes that use almost all pre-packaged ingredients that can take far less time.
The cake batter used in donauwelle is similar to that of pound cake. It is made from flour, butter, sugar and eggs. Once mixed, the batter is split into two equal portions and one portion is combined with cocoa powder to darken the color. A sheet pan is greased with butter and the plain half of the batter is poured in, followed by the darker batter.
Sour cherries, which can be found packaged in jars or cans, are drained and placed on top of the batter in the sheet pan. The cake is then baked until it is done. Before completing the cake, it needs to be cooled completely.
A simple buttercream with vanilla added to it is spread over the top of the cooled cake. At this point, it is refrigerated to set the buttercream and prepare it for the final step. Chocolate, either semisweet or bittersweet, is melted and allowed to cool but not harden. It is poured over the top of the buttercream to form a smooth, flat surface for the donauwelle. Once the chocolate is poured, the cake is refrigerated again until the chocolate hardens and sets, making the cake ready to serve.