Prep the pan and oven. Heat your oven to 375°F (190°C).
Line a 12-cup muffin tin with paper liners or lightly spray with oil. This recipe makes 12 muffins, which helps keep the calories under 100 each.
Whisk the dry ingredients. In a medium bowl, mix flours, sugar, baking powder, baking soda, and salt. Stir well to evenly distribute the leaveners.
Combine the wet ingredients. In another bowl, whisk the egg white until frothy.
Add Greek yogurt, milk, oil, vanilla, and lemon zest if using. Whisk until smooth.
Make the batter. Add the wet ingredients to the dry. Stir gently with a spatula just until the flour disappears.
The batter should be thick and slightly lumpy. Do not overmix or your muffins will be tough.
Fold in the berries. Toss berries with a teaspoon of flour (optional; helps prevent sinking), then fold them into the batter with as few strokes as possible. If using frozen berries, keep them frozen to minimize bleeding.
Portion the batter. Divide batter evenly among the 12 cups. Each should be about two-thirds full.
If using coarse sugar, sprinkle a pinch on top of each muffin.
Bake. Bake for 14–17 minutes, or until the tops are set and a toothpick comes out with a few moist crumbs. If your oven runs hot, start checking at 13 minutes.
Cool. Let muffins rest in the pan for 5 minutes, then transfer to a rack to cool completely. This helps them set and keeps the texture light.
Serve. Enjoy at room temperature or slightly warm.
For extra berry flavor, add a few fresh berries on the side.