For the topping, combine the flour, cinnamon, and brown sugar. Cut in the butter and mix until it resembles coarse crumbles. Set aside.

Preheat oven to 350. Beat butter until light an fluffy. Add in sugar and beat until mixed. Next, add in the eggs, one at a time. Once combined, add in vanilla and milk. Mix.

In a separate bowl, mix flour, baking powder, baking soda, salt, espresso powder, and cinnamon.

Alternately, to the wet ingredients, add in the dry mix and the sour cream. Start and end with dry mix.

The batter will be pretty thick, but that's what makes it so good. I used mini spring form pans, but this can easily be made in a 9-inch cake pan or 8x8 square pan. It can be made in something larger, the cake will just be thinner. Pour in half of the batter, then sprinkle some of the topping (somewhere between 1/4-1/2 of it) over the batter, and then pour the rest on top. Smooth out, and top with the rest of the remaining topping.

In mini spring form pans, these take about 35-40 minutes. In a cake pan, it takes closer to an hour.