Add the sugar, brown sugar, cinnamon, and flour. Mix until combined, then set aside.
For the Blueberry Cake
Preheat the oven to 350 degrees.
Beat together the sugar and softened butter until fluffy—about 2 minutes.
Add the egg and continue to beat for 1 minute.
Add vanilla, beat for about 30 seconds.
Mix together the dry ingredients for the cake (flour, salt, baking powder, baking soda) in a large bowl. Sprinkle in to the wet ingredients and beat until all the ingredients are combined—about 1 to 2 minutes.
Using a rubber spatula, add the sour cream. "Fold" it in by stirring the sour cream in, moving your spatula from the bottom to the top until the sour cream is fully incorporated.
Once incoporated, fold in the blueberries in the same way.
Grease an 8x8" pan with some butter. Scrape the cake mixture into the pan and even it out.
Sprinkle the crumb topping you made evenly on top.
Bake for 30 minutes, or until a toothpick comes out clean when poking the center of the cake.
Cut into 16 cubes and serve with a hot pot of coffee.
Don't want blueberries? Skip them and simply make a coffee cake without them! Or better yet, why not try it with raspberries?