Prepare the Crumb Topping:

1. Combine Dry Ingredients: In a medium bowl, mix the flour, brown sugar, and cinnamon.
2. Add Melted Butter: Pour in the melted butter and stir until the mixture resembles coarse crumbs. Set aside.

Prepare the Cake Batter:

3. Preheat Oven and Prepare Pan: Preheat your oven to 350°F (175°C) and grease a 9-inch square baking pan or line it with parchment paper.
4. Mix Dry Ingredients: In a bowl, whisk together the flour, baking powder, baking soda, and salt.
5. Cream Butter and Sugar: In a large mixing bowl, beat the softened butter and granulated sugar with an electric mixer until light and fluffy, about 2-3 minutes.
6. Add Eggs and Vanilla: Beat in the eggs, one at a time, followed by the vanilla extract.
7. Incorporate Sour Cream and Flour Mixture: Gradually mix in the flour mixture, alternating with the sour cream, starting and ending with the dry ingredients.
8. Fold in Chocolate Chips: Gently fold the chocolate chips into the batter using a spatula.

Assemble and Bake the Cake:

9. Spread Batter in Pan: Pour the batter into the prepared pan, spreading it evenly.
10. Add Crumb Topping: Sprinkle the prepared crumb topping evenly over the batter.
11. Bake: Bake for 50-55 minutes or until a toothpick inserted into the center comes out clean.
12. Cool: Let the cake cool in the pan for 15 minutes before transferring it to a wire rack to cool completely.