Preheat the oven to 350 degrees. Butter the sides and bottom of a glass 9x13 pan. You can use a metal pan, but the edges may get a bit crispy.

To make the crumb topping, mix both sugars, salt, and cinnamon in a medium bowl. Add the melted butter and whisk until combined. Fold in the flour until it is absorbed. Spread out a large sheet of parchment paper on the counter and spread this mixture out on the parchment paper to dry while you make the cake mixture.

To make the cake, sift the flour, baking powder, baking soda, and slat together in a medium bowl and set aside.

Cream the butter until it is smooth and ribbonlike in the bowl of a stand mixer fitted with the paddle. Scrape down the bowl and add the sugar. Beat until fluffy. Add the eggs, one at a time, and beat until incorporated. Scrape the bowl and mix again for 30 seconds. Add the sour cream and vanilla and beat just until incorporated. Add the dry ingredients in three parts, scraping down the bowl before each addition, beaiting only until it is just incorporated.

To assemble the cake, pour the batter in the prepared pan.Use your hands to scoop up a handful of the topping and make a fist. The topping should hold together. Break off in chunks and drop them over the cake. Repeat to use all the topping. Remember, the topping layer will look very thick.

Bake the cake for 45 to 55 minutes, or until a toothpick inserted in the middle comes out clean. Rotate the pan two times during the baking process. Cool the entire pan on a wire rack for 30 minutes before serving.

The cake will last for 3 days, tightly covered, at room temperature.