Preheat the oven to 350°F. Start by making the crumb mixture. In a food processor blend together the all-purpose flour, brown sugar, and ground cinnamon. Then cut the cold butter into cubes and add it to the processor. Pulse the butter with the rest of the ingredients for just a few seconds until the mixture is crumbly.

In a separate bowl, whisk together the 1½ cups all-purpose flour, baking powder, baking soda, and salt.

Blend the softened butter and granulated sugar together until well combined. Add the eggs and vanilla, then blend until combined. Now add the sour cream and briefly blend.

Add the dry ingredients to the wet ingredients and blend on low speed until just combined. The batter will be thick.

Line an 8x8 baking dish with parchment paper. Add half of the cake batter and spread it evenly.

In a small bowl, mix the granulated sugar and ground cinnamon together for the cinnamon sugar mixture.

Sprinkle the cinnamon sugar evenly over the first layer of cake batter.

Add the rest of the cake batter on top and spread it evenly without disturbing the cinnamon sugar layer.

Add the prepared crumb mixture evenly on top of the cake. Bake for 45-50 minutes or until a toothpick comes out clean.

Allow to cool for 15 minutes before lifting the parchment paper and slicing into 9 servings.