Preheat the oven to 350 degrees. Grease an 8 inch round cake pan and line the bottom with parchment paper. Set aside.
In a large bowl, beat together the butter, sugar, and sour cream until smooth. Beat in the eggs and clear vanilla until combined. Add in the flour, baking powder, salt, and sprinkles, and beat until combined and smooth. The batter will be thick.
Spread the batter into your prepared baking pan and bake for 12 minutes. While baking, make the crumb.
In a medium bowl, stir together all the ingredients with a fork. If your crumb isn't quite coming together, add a teaspoon of water at a time until you can form large crumbs with your fork.
After the cake has baked for 12 minutes, evenly and gently sprinkle the crumbs over the top of the partially baked cake. Return to the oven for another 20-22 minutes, or until a cake tester comes out clean. Cool and enjoy!