Preheat oven to 350°F. Grease and line a 10-inch square baking pan with parchment paper and set aside.
For the streusel, in a large bowl, combine the flour, brown sugar, ground cinnamon and salt. Add the butter and rub with your fingers until it resembles coarse crumbs. Set aside.
For the cake, in a large bowl, whisk together the flour, baking powder, and salt. In the bowl of a stand mixer, beat together the butter and both sugars until light and fluffy, about 3 minutes. Add the eggs and beat well after each addition. Stir in the sour cream and vanilla extract until well combined.
Add the dry ingredients and stir until just combined. Pour the batter into the prepared baking pan. Dollop with the cookie butter on top and then use a knife or skewer to swirl into the batter. Sprinkle the streusel topping evenly over the top.
Bake until golden brown and a toothpick, inserted in the middle, comes out clean, for 50 to 55 minutes. Remove from the oven and allow to cool for at least 30 minutes in the pan on a wire rack. Light the cake from the pan using the parchment paper and then slice into 9 or 12 squares. Serve and enjoy!