Preheat oven to 375º F. Grease or line muffin tin with liners.
Prepare streusel first. Stir together flour, sugar, and finely crushed Oreos in a small bowl. Cut in butter until consistency becomes like coarse meal. Refrigerate while you make the muffin batter.
Using an electric mixer, cream together butter and sugar until fluffy.
Add eggs, one at a time, stirring between additions until fully incorporated. Mix in the vanilla extract.
Mix in flour and baking powder until mostly combined. Add milk until everything is just incorporated. Batter will be thick.
Fold in crushed Oreos.
Divide batter between 15 muffin cups. Evenly sprinkle Oreo streusel over the muffins.
Bake 16-18 minutes, or until a tester comes out clean.
Remove from the oven and let cook for 5 minutes before removing to a wire rack to cool completely.
