Cream the butter in a standing mixer, and add both sugars. Continue to cream until light and fluffy; about 30 seconds. Add both eggs. Mix until well incorporated, and then add vanilla, baking powder, and salt. Give it anther good mix, and then add the flour. Mix until well incorporated, then add crushed Oreos. Stir gently until they are mixed in. Using a 2 tablespoon measure, scoop cookie dough onto a nonstick baking sheet and bake for 10 to 11 minutes at 375°F.  Cool on cookie sheet for five minutes, then transfer to a baking rack to cool completely.  Make the buttercream by beating the butter, sugar, Oreo cream, and vanilla until well incorporated. Fold in crushed Oreo cookies {without the cream center}. Pipe onto cooled cookies, and sprinkle with more crushed cookies.  Best served day of or next day; store in an airtight container for up to three days.  Enjoy! 🖤