3/4 stick (6 tablespoons) unsalted butter, melted and cooled
1 cup packed light brown sugar
1/2 cup whole milk
1 large egg
1 1/2 cups all-purpose flour
1 1/2 teaspoons baking powder
1 /4 teaspoon cinnamon
1/2 teaspoon salt
1 1/2 cups blueberries (7 1/2 oz)
Special equipment: a muffin pan with 12 (1/2-cup) muffin cups; 12 foil or paper muffin liners
Put oven rack in middle position and preheat oven to 400°F. Put liners in muffin cups.
In a large bowl whisk together butter, brown sugar, milk, and egg until combined well.
In a separate bowl, combine flour, baking powder, cinnamon, and salt.
Slowly add the dry ingredients to the wet ingredients and stir until just combined. Fold in blueberries gently.
Divide batter among muffin cups and bake until golden brown and a wooden pick inserted into center of a muffin comes out clean, 25 to 30 minutes.