Preheat the oven to 350 degrees F. Spray a 9x13-inch pan with baking spray.
In a large bowl, whisk together the flour, brown sugar, granulated sugar, salt, and cinnamon for the streusel. Add the melted butter and stir until it clumps together like sand.
In a separate large bowl, beat the butter and sugar on medium-high speed until creamy and light, about 2-3 minutes.
Add the eggs, one at a time, beating after each addition. Scrape down the side of the bowl and mix in the sour cream and vanilla extract.
Add the flour, baking powder, baking soda, and salt, mixing just until combined. The batter will be thick.
Spread 1/2 of the cake batter into the prepared pan. Sprinkle with half of the streusel, then dollop the remaining cake batter over this, using a knife to nudge the batter together to form a top layer as much as possible. Sprinkle the remaining streusel over the top layer of batter.
Bake for 50-55 minutes until golden brown on top and a toothpick inserted into the center of the cake comes out clean with just a few crumbs. Serve warm.