Preheat the oven to 350°F (177°C) and grease a 9×13-inch baking pan or line with parchment paper. You can use a glass, ceramic, or metal baking pan. The bake time is similar for each, but use a toothpick to test for doneness. Metal baking pans cook cakes faster. Set pan aside.
Mix the brown sugar, granulated sugar, cinnamon, and salt together in a medium bowl. Stir in the melted butter, then gently mix the flour using a fork. Keep the mixture as large crumbles, do not over-mix. If over-mixed, this will turn into a thick paste. Set aside.
Whisk the flour, baking soda, baking powder, and salt together. Set aside.
Using a handheld or stand mixer fitted with a paddle attachment, beat the butter and granulated sugar together on high speed until smooth and creamy, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Scrape down the sides and up the bottom of the bowl with a silicone spatula as needed. Add the eggs, sour cream, and the vanilla. Beat on medium-high speed until combined. The mixture may look curdled; that’s ok. Scrape down the sides and up the bottom of the bowl as needed. With the mixer on low speed, mix in the dry ingredients until smooth. Do not over-mix. The batter will be thick, creamy, and sticky. Spread the batter evenly into prepared baking pan. Top with crumb topping. Using a silicone spatula or the back of a large spoon, press the crumb topping tightly down into the cake so it sticks.
Bake for 45-55 minutes. Baking times vary, so keep an eye on yours and begin checking at 45 minutes. The cake is done when a toothpick inserted in the center comes out clean. If you find the top or edges of the cake is/are browning too quickly in the oven, loosely cover it with aluminum foil.
Remove the cake from the oven and set on a wire rack. Allow to slightly cool for at least 30-45 minutes before cutting. If desired, dust with confectioners’ sugar before slicing and serving. Use a sifter/fine mesh sieve.
