Preheat the oven to 350°F. Grease an 8" square pan with butter.

Beat the butter and sugar together until light and fluffy, about 6-7 minutes. Add eggs and vanilla, mixing just until combined.

Combine 1 cup flour and baking powder in a bowl. Sprinkle peaches with a few tablespoons of this mixture plus cinnamon; gently stir to coat.

Add half the dry ingredients to the butter mixture, stir to combine. Add sour cream, mix again, then add remaining dry ingredients. Mix just until combined. Stir in peaches and pour into prepared pan.

In a small bowl, combine topping flour and brown sugar. Add melted butter and stir lightly with a fork, leaving large crumb pieces. Sprinkle over batter.

Bake for 44-46 minutes until a toothpick comes out clean or with moist crumbs. Let cool before slicing.