Whisk together the flour, baking powder, and baking soda in a mixing bowl.

In the bowl of an electric mixer, cream together the butter and brown sugar until light and fluffy, about 3 minutes. Add the eggs, one at a time, beating well after each addition. Beat in the vanilla. Turn the mixer to low, add half the flour mixture, then the sour cream, and finally the rest of the flour. Beat just until everything is combined. The batter will be stiff. Scrape the batter into the prepared skillet. Prepare the topping and sprinkle it evenly over the cake. Bake for 35 – 40 minutes or until a toothpick inserted into the center comes out clean.

Combine the brown sugar, flour, cinnamon, and salt in a small mixing bowl. Add the butter and work it into the flour mixture with your fingers until well blended.