Finely crush 30 Oreos in a food processor.

Stir Oreo crumbs with ½ c. softened butter and press into 9x9 inch pan.

Chill until cold.

In a mixer on low, beat powdered sugar, ½ c. softened butter, milk, and vanilla.

Beat for a few minutes until fluffy.

Crush the other 10 Oreos, not too fine, and stir into the buttercream.

Spread frosting over crust and chill until serving time. Cut into bars!