Donauwelle (Danube Wave Cake)

Instructions

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1. 1 Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C). Line a 9x13-inch baking dish with parchment paper.
2. 2 To make the cake layers: Sift flour and baking powder together into a bowl; set aside. Beat 1 cup plus 2 tablespoons butter with an electric mixer in a large bowl until light and fluffy. Beat in white sugar, vanilla extract, and 5 egg yolks. Stir in flour mixture until just combined.
3. 3 Beat egg whites in a glass, metal, or ceramic bowl until foamy; continue to beat until stiff peaks form. Lift your beater or whisk straight up: the egg whites should form a sharp peak that holds its shape.
4. 4 Gently fold 1/3 of the egg whites into the batter, keeping as much volume as possible. Add the remaining egg whites, folding just until incorporated.
5. 5 Pour half of the batter into a separate bowl. Sift cocoa powder into one bowl of batter; stir until just combined.
6. 6 Pour white cake batter into the prepared baking dish, then spread chocolate cake batter on top. Pat cherries dry with paper towels, and sprinkle them evenly on top.
7. 7 Bake in the preheated oven until a toothpick inserted into the center of the cake comes out clean, 25 to 30 minutes; set aside to cool.
8. 8 To make the custard filling: Whisk cornstarch and 1/2 cup sugar together in a small bowl. Heat milk in a small saucepan just until hot but not boiling. Whisk in cornstarch mixture until smooth; bring mixture to a boil, whisking constantly, until mixture is thick and easily coats the back of a spoon, about 2 to 3 minutes. Remove from heat and stir in vanilla.
9. 9 Spread custard filling over cooled cake; press a piece of plastic wrap directly onto the surface of the custard filling so it doesn't form a skin. Refrigerate until set, at least 2 hours to overnight.
10. 10 To make the chocolate glaze: Place chocolate chips in a microwave-safe bowl. Heat at 30 second intervals, stirring each time, until just melted and smooth. Stir in oil until glossy.
11. 11 Spread chocolate glaze over chilled custard layer. When the glaze has set slightly, about 10 minutes, drag a fork lightly across the surface in wavy lines to create a wave pattern on the chocolate.
12. 12 Let glaze set completely before slicing cake into squares. Enjoy!