Preheat oven to 350°F. Grease a 9x13-inch baking dish.

In a medium bowl, sift together 2.5 cups flour, baking powder, baking soda, and salt.

In a large bowl, cream the softened butter and sugar until fluffy.

Add eggs one at a time, beating well after each addition. Mix in sour cream and vanilla.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Pour batter into the prepared baking dish and smooth the top.

In a bowl, combine light brown sugar, sugar, salt, and cinnamon. Add melted butter and mix until crumbly.

Stir in flour until combined and sprinkle evenly over the batter.

Bake for 50 to 55 minutes until a toothpick inserted into the center comes out clean.

Allow cake to cool before serving. Slice into 24 pieces.