For the cake:
For the syrup:
For the cream:
1. Make the cake: Preheat oven to 350F (175C). Line three 8-inch round cake pans with parchment and, grease with butter and dust either flour. set aside.
2. In a large bowl whisk eggs and sugar, until doubled in volume, about 5-6 minutes. in a separate bowl stir sour cream with baking soda, then add to the egg mixture and beat until incorporated. add dulce de leche and beat until incorporated.
3. Sift flour, baking powder and salt. Stir until incorporated. Do not overmix.
4. Divide the butter between the pans. Bake for 16-18 minutes, or until a toothpick inserted in the center comes out clean. Remove from the oven and let cool for 5-10 minutes, release from the pan and let cool completely. then, cut the tops of the cakes. Cut into small cubes and bake at 400F (200C) for 10 minutes, until golden brown. Set aside for later.
5. Make the syrup: in a small saucepan heat water, milk, sugar, coffee and liquor. Bring to a simmer until the sugar is dissolved, set aside.
6. Make the cream: in a large bowl beat butter until cream cheese until smooth. Add dulce de leche and beat until incorporated and smooth. In a separate bowl neat heavy cream to medium peaks. Fold the whipped cream into the butter mixture. Transfer to a piping bag (optional).
7. Assembly: place first cake layer (cut side up) in the middle of the platter, soak with the syrup. Spread/pipe a layer of the cream, sprinkle 1-2 tablespoons of crushed hazelnuts. Repeat: place the second layer of cake, soak with syrup, spread another layer of cream, sprinkle hazelnuts. Place third layer of cake (cut side down), soak with syrup. Spread the remaining cream over top and the sides of cake.
8. Place baked leftover cake pieces in a food processor and process into small crumbs. Decorate the cake with the crumbs.
9. Refrigerate for at least 3 hours before serving.