Buttery, soft, and moist blueberry muffins bursting with juicy berries and crowned with a crunchy cinnamon–brown sugar streusel, baked to tall bakery-style domes.
Preheat oven to 425°F (218°C). Line or grease a 12-cup muffin pan and set aside.
Make the topping: In a small bowl, combine brown sugar, chopped walnuts (or pecans), and cinnamon; set aside.
Whisk the flour, baking soda, baking powder, and salt together in a large bowl; set aside.
With a mixer, cream the butter, granulated sugar, and brown sugar on high speed until smooth and creamy, about 3 minutes.
On medium speed, beat in the eggs one at a time, then mix in the sour cream (or yogurt) and vanilla until combined.
With the mixer on low, add the dry ingredients and milk; mix just until combined. Batter will be thick and creamy.
Fold in the blueberries.
Divide batter evenly among muffin cups, filling to the top. Sprinkle each with streusel, pressing gently so it adheres.
Bake for 5 minutes at 425°F (218°C), then (without opening the oven) reduce the temperature to 350°F (177°C) and bake 18–20 minutes more, or until a toothpick inserted in the center comes out clean.
Cool in the pan for 5 minutes, then transfer muffins to a wire rack to cool. Store covered at room temperature for a couple days, refrigerated up to 1 week, or freeze up to 3 months.