Combine brown sugar, flour, cinnamon, and salt in a bowl.
Add the butter, and stir until combined. Then Set aside.
Preheat oven to 350°F. Line a 9" springform pan with parchment paper to hang on the long sides. Coat paper with melted butter.
Whisk together flour, baking powder, baking soda, and salt. Set aside.
Using a stand mixer on medium speed, beat butter and sugar until light and fluffy. Add eggs, one at a time, mixing after each addition. Mix in the vanilla.
Reduce stand mixer speed to low. Mix in the flour mixture in three portions, alternating with sour cream. Mix until combined.
Transfer the batter to the prepared pan, and spread evenly.
Sprinkle the topping over the top.
Bake 30 to 35 minutes, or until a pick inserted into the center comes out clean.
Cool the cake on a wire rack for about 15 minutes. Then use the parchment paper, lift the cake out of the pan to cool completely on a wire rack.