Preheat oven to 350F (175C) and lightly grease a 9x9” (23x23cm) metal pan with butter. Set aside.

In a small mixing bowl, whisk together sugar, cinnamon, and salt for the ripple and set aside.

Combine butter and sugar in a large mixing bowl and use an electric mixer to beat together until light and fluffy.

Add eggs and beat until completely combined.

Add sour cream and vanilla extract and stir well. Pause periodically to scrape down the sides and bottom of mixing bowl with a spatula to ensure all ingredients are well incorporated.

In a separate, medium-sized mixing bowl, whisk together flour, baking powder, baking soda, and salt.

Gradually fold dry ingredients into wet ingredients until batter is uniform.

Spread approximately half (slightly less than half is best) of the batter evenly into the bottom of your prepared pan, then sprinkle the cinnamon/sugar ripple mixture over the batter. Dollop the remaining batter over the ripple layer and gently spread into an even layer over the surface. Prepare the streusel topping.

Combine flour, sugars, cinnamon, and salt In a medium sized bowl and whisk until combined.

Pour melted, cooled butter over the flour mixture and use a fork to toss / claw together the mixture until you have a crumbly streusel mixture (all the butter should be absorbed and no dry flour should be remaining).

Sprinkle streusel evenly over prepared batter.

Bake in center rack of 350F (175C) oven for 50 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs.

Allow to cool before cutting and serving.