In a large bowl cream the butter and sugar until fluffy.
Add the eggs, sour cream, and vanilla.
Sift together the flour, baking powder, and salt.
Slowly mix the dry ingredients into the wet ingredients until combined.
Pour cake batter into the desired baking dish, we use a springform pan.
In a separate bowl mix together the topping ingredients.
Top batter with crumb topping
Bake for 35 minutes or until a toothpick inserted into the cake comes out clean.
Notes
When checking your cake with a toothpick make sure you're checking towards the center as the outer edges will cook much quicker than the center of the cake.