Blueberry-Sour Cream Muffins

Preheat oven to 425 °. Place 12 muffin-cup liners in muffin cups. Lightly coat liners with cooking spray. Combine oats, brown sugar, 1 tablespoon flour, and cinnamon in a bowl. Drizzle with 1 tablespoon melted butter; toss with a fork. Weigh or lightly spoon 2 cups flour into dry measuring cups; level with a knife. Combine flour, baking powder, salt, and baking soda in a bowl, stirring well with a whisk. Place remaining 2 tablespoons butter, sour cream, granulated sugar, oil, vanilla, and egg in a bowl; stir with a whisk. Add sour cream mixture to flour mixture; stir just until combined. Fold in blueberries. Divide batter evenly among prepared muffin cups. Sprinkle evenly with topping. Bake at 425 ° for 5 minutes. Reduce oven temperature to 375 °; bake an additional 13 minutes or until a wooden pick inserted in center comes out clean. Cool muffins in pan for 5 minutes. Remove from pan; cool completely on a wire rack.