Preheat and prep: Heat your oven to 400°F (200°C).
Line a 12-cup muffin tin with paper liners or grease well.
Mix dry ingredients: In a large bowl, whisk flours, protein powder, baking powder, baking soda, salt, and cinnamon until evenly combined. This helps avoid clumps of protein powder.
Combine wet ingredients: In a separate bowl, whisk Greek yogurt, milk, eggs, oil, sweetener, vanilla, and lemon zest until smooth.
Bring the batter together: Pour wet ingredients into the dry. Stir gently with a spatula until just combined.
The batter should be thick but scoopable. Do not overmix.
Fold in berries: Add blueberries and fold in carefully. If using frozen berries, add straight from the freezer to minimize color bleed.
Fill the tin: Divide batter among the 12 cups, filling each about 3/4 full. For taller domes, you can fill them closer to the top.
Top (optional): Sprinkle with coarse sugar or add a couple of extra blueberries on top for a bakery look.
Bake hot, then reduce: Place the tray on the middle rack and bake at 400°F (200°C) for 5 minutes.
Without opening the oven, reduce heat to 350°F (175°C) and bake 12–15 more minutes, until a toothpick comes out clean or with moist crumbs.
Cool: Let muffins rest in the pan 5 minutes, then transfer to a wire rack. Cooling helps set the crumb and prevents soggy bottoms.
Enjoy: Serve warm or at room temp. They pair great with coffee, tea, or a smear of almond butter for extra protein.