How to Make It
Preheat oven to 400°. Coat a 12-cup muffin tin with cooking spray or line with paper liners, if you prefer.
Combine sugar and lemon zest in the bowl of a food processor; pulse until zest is incorporated into sugar and fragrant. Add buttermilk, oil, vanilla, and egg to processor; pulse until just combined.
Combine flours, baking powder, baking soda, and salt in a large bowl, stirring with a whisk. Add the buttermilk mixture to bowl and stir gently until almost blended. Gently divide batter equally among 3 separate bowls; fold raspberries into 1/3 of batter, blueberries into another 1/3 of batter, and strawberries into remaining 1/3 of batter. Equally divide the batters among prepared muffin cups.
Bake at 400° until golden brown, about 16 to 18 minutes. Let muffins cool in pan for 5 minutes before turning out onto a wire rack.