Preheat and prep: Heat your oven to 375°F (190°C). Line a 12-cup muffin pan with paper liners or grease it lightly. This helps prevent sticking and gives you taller muffin tops.

Make oat flour (optional): If you like a heartier, moist crumb, pulse 1 cup of rolled oats in a blender until fine. You can also use store-bought oat flour. Using whole oats works too, but the texture will be a bit more rustic.

Whisk the dry mix: In a large bowl, whisk 1 cup all-purpose flour, 1 cup oat flour, 1/2 cup protein powder, 1/3 cup sugar, 2 teaspoons baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon salt. Break up any protein powder lumps so the batter stays smooth.

Combine the wet ingredients: In a separate bowl, whisk 1 cup Greek yogurt, 1/2 cup milk, 2 large eggs, 1/4 cup oil, and 2 teaspoons vanilla. If using lemon zest, add 1–2 teaspoons now. The yogurt keeps the batter creamy and prevents overmixing.

Bring it together: Pour the wet ingredients into the dry. Stir gently with a spatula until just combined. The batter should be thick but scoopable. A few streaks of flour are okay.

Fold in the berries: Toss 1–1 1/2 cups blueberries with a teaspoon of flour to help prevent sinking, then fold into the batter with minimal stirring. If using frozen berries, don’t thaw; fold them in straight from the freezer.

Fill the muffin pan: Divide the batter evenly among the cups, filling each about 3/4 full. For a bakery-style top, mound the batter slightly. Sprinkle with coarse sugar if you want a crunchy lid.

Bake: Bake 16–20 minutes, until the tops are set and lightly golden and a toothpick comes out with a few moist crumbs. Check at 16 minutes to avoid drying them out.

Cool: Let muffins cool in the pan for 5 minutes, then move to a rack. Cooling helps them set so they don’t crumble when you peel the liner.

Enjoy: Serve warm or at room temperature. These pair well with a smear of almond butter if you want even more protein and healthy fats.