Beat 4 eggs (no need to separate them) with sugar until it’s three times in volume.
Whisk sour cream together with dulce de leche, until you reach the same consistency.
Fold sour cream mixture into whipped eggs.
In a separate dish, combine baking soda with lemon juice, add to the batter.
Combine flour together with baking powder. Using a spatula, fold in flour by thirds; be very gentle with the dough, so you don't over mix and lose the fluffiness. Spray a 7 or 9 inch cake pan with cooking spray.
Place half of the batter into a baking pan. If you have another pan in the same in size, repeat with the remaining batter. If you don't have a pan, after baking the first layer, use the same pan.
Bake at 350F for 30 minutes. Use a toothpick to check if the cake is baked. Once the cake cools, cut the cake into two slices.
Cmmbine whipping cream with condensed milk. Soak the inside of all slices with the sweetened cream. In the meantime, dice toasted hazelnuts and set aside.