1 1/2 cups all-purpose flour (spooned and leveled)
2/3 cup oat bran
2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon ground cinnamon
1/4 teaspoon fine salt
6 tablespoons unsalted butter, room temperature
1/2 cup plus 1 tablespoon sugar
2 large eggs
2 teaspoons pure vanilla extract
1 cup buttermilk
1 1/2 cups chopped blackberries
1. Preheat oven to 375 degrees. Line 12 standard muffin cups with paper liners. Whisk together flour, oat bran, baking powder, baking soda, cinnamon, and salt.
2. In a large bowl, using a mixer, beat butter and 1/2 cup sugar on high until light and fluffy, about 6 minutes. Beat in eggs and vanilla until combined. With mixer on low, add flour mixture in 2 additions, alternating with buttermilk, and beat until combined. Fold in blackberries.
3. Divide batter among muffin cups and sprinkle with remaining 1 tablespoon sugar. Bake until a toothpick inserted in center of a muffin comes out with moist crumbs attached, 20 to 25 minutes, rotating pan halfway through. Let cool in pan on a wire rack 5 minutes, then transfer muffins to rack and let cool completely.