To begin, preheat your oven to 375 degrees. Line a standard muffin tin with papers and set it aside.
In a bowl, stir together the flour, baking powder, and salt. Set it aside.
In your mixing bowl, beat together the brown sugar, butter, and peanut butter. Mix in the eggs. Stir half of the flour mixture. Mix in the milk and vanilla extract. When combined, mix in the remaining flour mixture. Gently fold in the Reese's.
Scoop the batter into the muffin tin. Sprinkle about a half teaspoon of the raw sugar on top of each muffin. Bake 19-20 minutes or until they test done with a toothpick. Cool on a rack.