Preheat oven to 375F and line 18 cupcake wells with paper liners.
Cream softened butter for 2-3 minutes until fluffy, then add sugar and mix 2 minutes until pale.
Mix in eggs one at a time, then add vanilla.
Whisk together flour, baking powder, and salt in a separate bowl.
Add half the milk to butter mixture and stir, then add half the flour mixture and mix until just combined.
Add remaining milk, stir, then add remaining flour and mix until just incorporated.
Crush Oreos into chunky pieces and fold into batter.
Divide batter between cupcake wells, filling each 2/3 full.
Bake 15-17 minutes until toothpick comes out with moist crumbs and tops spring back when touched.
Cool in pan 5 minutes, then transfer to wire rack to cool completely before frosting.