1. Preheat Oven and Prepare Muffin Pan: Start by preheating your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or lightly grease each cup with non-stick spray. This prevents sticking and makes for easy cleanup.

2. Combine Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, vanilla protein powder, granulated sugar, baking powder, and salt. Make sure there are no lumps and all ingredients are evenly distributed.

3. Mix Wet Ingredients Separately: In a medium bowl, whisk the large egg, milk, unsweetened applesauce, melted coconut oil (or vegetable oil), and vanilla extract until well combined and smooth.

4. Combine Wet and Dry Mixtures: Pour the wet ingredients into the bowl with the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are perfectly fine and will lead to tender muffins. Overmixing can result in tough muffins.

5. Fold in Blueberries: Gently fold in the fresh or frozen blueberries. If using frozen, add them directly from the freezer to the batter. Distribute them evenly throughout the mixture.

6. Fill Muffin Cups: Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full. For a uniform look, you can use an ice cream scoop.

7. Bake Until Golden: Bake for 20-25 minutes, or until the tops are golden brown and a wooden skewer or toothpick inserted into the center of a muffin comes out clean.

8. Cool Before Serving: Remove the muffin tin from the oven and let the muffins cool in the pan for 5 minutes before transferring them to a wire rack to cool completely. This helps prevent them from getting soggy on the bottom.