1. Preheat oven to 350 F. Coat the sides and bottom of a glass 9" × 13" baking dish with non-stick cooking spray.

Crumb Topping:

1. Mix both sugars, salt, and cinnamon in a medium bowl with a fork.
2. Add the melted butter and stir until combined. Fold in the flour until it is absorbed.
3. Spread out the crumb mixture on a baking sheet to dry while you make the cake mixture.

Cake:

1. Sift together the flour, baking powder, baking soda, and salt in a medium bowl; set aside.
2. In a large bowl, cream butter until pale and smooth. Add sugar, and beat till fluffy. Add the eggs one at a time, beating between each addition. Add in the sour cream and vanilla; beat until smooth.
3. Add flour mixture in 2 additions, beating just until incorporated after each addition. Once the batter is smooth, it's ready.
4. Pour the batter in the prepared pan. Using a spatula, spread batter evenly in baking dish.
5. Using your hands, scoop up a handful of the crumb topping, make a fist so that it holds together, then break off chunks and drop over the cake. Repeat until all the topping is used up. You will have a thick layer of topping.
6. Bake for 45 minutes, or until a toothpick inserted comes out clean. Cool on wire rack. Serve at room temperature.