Preheat oven to 350 degrees Fahrenheit.

Grease a 9x13 baking dish with butter.

In a bowl, sift together the flour and baking powder.

Cream the softened butter with sugar until fluffy.

Add eggs one at a time, mixing well after each.

Mix in sour cream and vanilla extract.

Gradually add the flour mixture and mix until combined.

Pour batter into prepared dish and set aside.

For topping, mix brown sugar, flour, cinnamon, and melted butter until crumbly.

Sprinkle topping over batter in baking dish.

Bake for 55 minutes until golden.

Allow to cool before serving.