Blueberry Muffins

Topping:
- 1/2 cup packed brown sugar
- 1/2 cup chopped walnuts or pecans
- 1 tsp cinnamon

Muffins:
- 1 3/4 cups all-purpose flour
- 1 tsp baking soda
- 1 tsp baking powder
- 1/2 tsp salt
- 1/2 cup unsalted butter, softened
- 1/2 cup granulated sugar
- 1/4 cup packed brown sugar
- 1/2 cup sour cream or yogurt
- 2 large eggs
- 1 1/2 tsp vanilla extract
- 1/4 cup milk
- 1 1/2 cups blueberries (fresh or frozen)

Steps:
- Preheat oven to 425 F; line a 12-count muffin pan. Mix the topping and set aside.
- Whisk the dry ingredients. Beat butter and sugars until creamy; add sour cream, eggs and vanilla. Mix in the dry, then the milk; fold in blueberries.
- Fill liners to the top, press the topping on gently.
- Bake 5 minutes at 425 F, then 350 F for 16-19 more, until a toothpick comes out clean.