Preheat your oven to 350°F (175°C) and grease an 8-inch square pan or line it with parchment paper.

In a bowl, combine 1 cup of all-purpose flour, ½ cup each of granulated sugar and brown sugar, and 1 teaspoon of cinnamon. Cut in ½ cup of cold butter until crumbly, then refrigerate.

In a large bowl, whisk together 1 cup of sour cream, 2 eggs, 1 cup of granulated sugar, and 1 teaspoon of vanilla until smooth.

In another bowl, whisk together 2 cups of flour, 1 teaspoon of baking powder, ½ teaspoon of baking soda, and 1 teaspoon of cinnamon. Gradually combine with wet ingredients.

Pour half the batter into the pan, smooth it out, and sprinkle half of the crumb topping over it.

Dollop the remaining batter over the crumb layer and sprinkle the rest of the topping on top.

Bake for 30-35 minutes until a toothpick comes out clean. Let it cool in the pan.

If desired, prepare icing by whisking powdered sugar with a splash of milk, and drizzle it over the cooled cake.