Preheat your oven to 350°F (175°C).

Grease and flour a 9-inch square baking pan.

In a medium mixing bowl, combine 1 1/2 cups of all-purpose flour, baking powder, baking soda, and salt. Whisk together.

In a large bowl, cream together the softened butter and granulated sugar using an electric mixer on medium speed until light and fluffy, about 2 to 3 minutes.

Add the eggs one at a time, beating well after each addition. Add the vanilla extract and mix until incorporated.

Gradually add the flour mixture to the butter mixture, alternating with the sour cream. Start and end with flour, mixing gently until just combined.

In a separate bowl, combine the brown sugar, ground cinnamon, and 1/4 cup flour for the crumb topping, and mix well.

Pour the batter into the prepared baking pan and smooth it into an even layer.

Sprinkle the crumb topping evenly over the batter.

Bake in the preheated oven for 40 to 45 minutes, or until a toothpick inserted in the center comes out clean.

Remove from the oven, let it cool for about 10 minutes, then transfer to a wire rack to cool completely.

Once cooled, cut the cake into squares and serve.