Heat oven to 350°F. Place paper baking cups into 24 muffin pan cups. Set aside.
Combine brownie mix, butter and eggs in medium bowl. Beat at medium speed, scraping bowl often, until well blended. Stir in mint pieces.
Spoon heaping tablespoonfuls of batter into prepared muffin cups. Bake for 20 to 25 minutes or until surface is set and glossy. Cool 5 minutes; remove from pans.
Variation: Miniature Brownie Cups: Place foil mini muffin cups into mini muffin pans or onto cookie sheet. Spoon about 2 teaspoons batter into each cup. Bake for 15 to 18 minutes.
These brownie snack cups can be frosted or served à la mode with your favorite ice cream.