Semi-homemade Blueberry Muffins

I love the boxed blueberry muffins mixes...the ones that have the blueberries in a can that you have to rinse and drain. The blueberries are tiny tiny...I love tiny blueberries.
I especially the muffin mixes that come with a crumb topping. Have you seen those? The crumb topping makes all the difference to a bland muffin. 
 Unfortunately, my grocers do not carry blueberry muffin mixes with the crumb topping...What's up with that?!
Anyway, it doesn't matter, because I can make my own crumb topping right at home and add it to those boring, bland, boxed muffins :)

After preparing your muffins, simply combine the following ingredients until crumbly. 
Then sprinkle on top and bake as directed.

1/2 cup sugar
1/4 cup flour
2 tablespoons cold butter