1. Preheat and Prepare: Start by preheating your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or lightly grease each cup. This step ensures your muffins won’t stick and makes for easy cleanup.

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

3. Mix Wet Ingredients: In a separate medium bowl, whisk together the milk, unsweetened applesauce, vegetable oil, large egg, and vanilla extract until well combined. The mixture should look smooth and uniform.

4. Gently Combine Wet and Dry: Pour the wet ingredients into the bowl with the dry ingredients. Stir with a spoon or spatula just until the flour mixture is moistened. It’s crucial not to overmix; a few lumps are perfectly fine. Overmixing can lead to tough, dry muffins.

5. Fold in Add-ins (Optional): If you’re using chocolate chips or berries, gently fold them into the batter until they are just evenly distributed. Again, avoid overmixing to maintain a tender crumb.

6. Fill Muffin Cups: Divide the batter evenly among the 12 prepared muffin cups. Each cup should be about two-thirds full.

7. Bake Until Golden: Place the muffin tin in the preheated oven and 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 Enjoying: 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 becoming soggy on the bottom.