Sponge Cake

Cup of Yum
1. Beat the eggs and sugar together until the mixture has tripled in volume.
2. In a separate bowl, whisk the sour cream and dulce de leche together until well combined.
3. Fold the sour cream mixture into the beaten eggs.
4. In a small bowl, combine the baking soda and lemon juice. Mix it into the batter.
5. Combine the flour and baking powder, then fold it into the batter in thirds. Take care not to overmix. 
6. Grease two 9-inch cake pans with cooking spray. Distribute the batter evenly among the cake pans and spread it out into a smooth layer.
7. Bake the cakes at 350°F for 30 minutes. Use a toothpick to check if the cake is baked — it should emerge clean or with only a few crumbs. Allow the cakes to cool completely, then cut each one in half horizontally so you have four layers total.

Cake Soak

1. Whisk together the heavy whipping cream with the sweetened condensed milk. Set aside.

Dulce De Leche Cream

1. Beat together the softened butter and dulce de leche until creamy.
2. In a separate bowl, whisk the cold heavy cream until soft peaks form. Avoid overbeating.
3. Gently fold together the dulce de leche mixture and whipped cream.

Layering the Cake

1. Place one cake layer on the serving platter and brush it with the cake soak. Spread on the dulce de leche cream, then sprinkle on a handful of chopped hazelnuts. Add the second cake layer, then repeat the process with the soak, cream, and hazelnuts. Repeat until all the cake layers are used up.
2. Decorate the outside of the cake with the remaining dulce de leche cream, then press chopped hazelnuts onto the sides and add whole hazelnuts on top.