Combine first 5 ingredients in a large bowl; beat with a mixer at medium speed until well blended.
Lightly spoon flour into dry measuring cups; level with a knife. Add flour and mint to butter mixture; stir just until combined. Turn dough out onto a floured surface; knead lightly 5 times.
Pat dough into an 8-inch circle on a baking sheet coated with cooking spray. Cut dough into 12 wedges, cutting into but not through dough. Crimp edges of dough with a fork. Bake at 350° for 25 minutes or until golden. Sprinkle with 2 teaspoons powdered sugar.