Sour Cream Blueberry Muffins

I've probably made this recipe hundreds of times over the years.  It's an original "keeper".

2 cups Bisquick

 1/4 cup sugar

1/2 teaspoon cinnamon
1 cup sour cream (one 8 oz. carton)

1 egg
1 cup blueberries, drained (one 15 oz. can)

(I actually prefer the canned to fresh; they mush a bit and add flavor to the muffin dough)

1. Mix the Bisquick, sugar and cinnamon together.
2. Mix the egg and sour cream together (vanilla yogurt also works).
3. Add the egg mixture all at once to the Bisquick mixture. Batter will be stiff. If the dough is too dry add a tablespoon of water or milk.
4. Fold in blueberries.
5. Fill muffin tins almost full.
6. Sprinkle sugar on top.
7. Bake at 350 degrees for 10 - 20 minutes or until just firm to touch.
8. They freeze well.