Preheat the oven at 375 F degrees.
In a mixer, add 2 of the eggs and 1/2 cup of the sugar and mix well until light and fluffy. Add the sour cream and the melted butter and mix well. Add the flour and the baking powder, and mix well.
In another bowl mix the ricotta with the remainder of the sugar, vanilla extract and the remaining 2 eggs and mix well. You may also add raisins with ricotta if you wish. Personally I like a few raisins in this cake, so now would be the time to add about 1/2 cup of raisins.
You can use a cheesecake pan, butter it well. Pour the cake batter first, then pour the ricotta mix in the middle. Do not mix. Bake for about 30 to 45 minutes or until golden brown. Let cool before serving. You may also sprinkle some powdered sugar on top of the cake.