Preheat your oven to 350°F (175°C). Line a muffin tin with liners or lightly grease it.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, protein powder, and brown sugar.
In another bowl, whisk together the melted butter, eggs, milk, Greek yogurt, and vanilla extract.
Gradually add the wet ingredients into the dry ingredients, stirring until just combined.
Fold in 1.5 cups of chocolate chips.
Scoop the batter evenly into the prepared muffin tin, filling each about ¾ full.
Sprinkle the remaining ½ cup of chocolate chips and coarse sugar on top.
Bake for 18–20 minutes (or 12–14 minutes for mini muffins), until a toothpick inserted in the center comes out clean.
Let them cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.