Whisk flour, baking soda, baking powder, and salt.
Beat butter, peanut butter, granulated sugar, and brown sugar until fluffy.
Mix in egg, vanilla, and milk.
Stir in dry ingredients just until combined.
Chill dough 20 minutes for easier rolling.
Combine coating sugar, cinnamon, and a pinch of nutmeg.
Scoop 1½-tablespoon portions; roll into balls.
Toss balls in cinnamon sugar to coat.
Arrange on sheets, spaced 2 inches apart.
Gently flatten tops with your fingers.
Bake 9 to 11 minutes, until edges set.
Cool 5 minutes, then move to racks.
Notes
Want extra peanut crunch? Swap creamy for crunchy peanut butter. No nutmeg? Use pumpkin pie spice or skip it. To make them chewier, chill 45 minutes. Prefer gluten-free? Use a 1:1 baking blend and add 1 extra tablespoon milk if the dough feels dry.