Mix all ingredients, except for the blueberries. Lightly fold in the blueberries.
Spoon batter into cupcake cups, filling cups ½-¾ of the way.
For the topping: Combine sugar and flour. Using a fork blend in butter until topping resembles clumping sand. Sprinkle a tablespoon of topping into each cupcake cup.
Bake at 350° for 18 - 20 minutes.
Notes
If you don't have any buttermilk, you can substitute regular milk.