Preheat your oven to 375°F (190°C) and line a standard 12-cup muffin tin with paper liners or coat generously with cooking spray.

In a large bowl, whisk together the flour, protein powder, sugar, baking powder, and salt until thoroughly combined.

In a separate medium bowl, whisk the milk, egg, melted butter, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and stir gently with a spatula until just combined. The batter should still have a few small lumps.

Gently fold in the cooked and crumbled breakfast sausage until evenly distributed.

Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full.

Bake for 15-18 minutes until the tops are golden brown and a toothpick inserted comes out clean.

Let the muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely.

If using the maple glaze, whisk together the powdered sugar, maple syrup, and milk until smooth, then drizzle over the cooled muffins.