1. Preheat your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or grease it thoroughly with non-stick spray.

2. In a large mixing bowl, whisk together the all-purpose flour, protein powder, granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps and everything is evenly distributed.

3. In a separate medium bowl, whisk together the milk, unsweetened applesauce, melted coconut oil (or vegetable oil), large egg, vanilla extract, lemon zest, and fresh lemon juice until well combined and smooth.

4. Pour the wet ingredients into the dry ingredients. Stir with a spatula or wooden spoon just until barely combined. It’s crucial not to overmix; a few lumps are perfectly fine. Overmixing leads to tough muffins.

5. Carefully fold in the fresh or frozen blueberries. If using frozen, do not thaw them first, as this can bleed color into the batter. Gently incorporate them until they are evenly distributed throughout the batter.

6. Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full. You can use an ice cream scoop for consistent sizing.

7. Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of a muffin comes out clean. The tops should be golden brown and spring back when lightly touched.

8. Once baked, remove the muffin tin from the oven and let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely. This prevents them from getting soggy on the bottom.