Step 1

Preheat oven to 400 degrees F. Line a 12-cup muffin pan with paper liners or coat muffin cups with cooking spray.

Step 2

To prepare crumb topping: Combine 1/4 cup flour, 1/4 cup brown sugar, 1 teaspoon lemon zest and 1/8 teaspoon salt in a small bowl. Add 2 tablespoons oil and stir until crumbly. Set aside.

Step 3

To prepare muffins: Whisk whole-wheat flour, all-purpose flour, baking powder, baking soda and salt in a medium bowl. Whisk eggs and brown sugar another medium bowl until blended. Add buttermilk, oil, lemon zest and vanilla (or lemon) extract; whisk until well combined. Make a well in the center of the dry ingredients and pour in the wet ingredients; stir until just combined. Add blueberries and stir until just combined. Divide the batter among the muffin cups. Sprinkle with the crumb topping, gently pressing to adhere.

Step 4

Bake the muffins until golden brown and a wooden skewer inserted in the center comes out clean, about 20 minutes. Let cool in the pan for 10 minutes, then remove to a wire rack and let cool for at least 5 minutes before serving.