PREPARE and bake brownie mix in 8-inch square baking pan as directed on package. Remove from oven. Immediately use round handle of wooden spoon to poke holes at 1-inch intervals down through warm brownies to bottom of pan.
POUR milk into large bowl. Add dry pudding mix. Beat with wire whisk 2 min. or until well blended. Immediately pour about 1/2 of the thin pudding mixture evenly over warm brownies. Tap pan lightly to fill holes. Let remaining pudding stand at room temperature to thicken slightly; spread over top of brownies to "frost" brownies.
REFRIGERATE at least 1 hour. Cut into 2-inch squares, then cut each square diagonally in half to form 2 triangles. Store in tightly covered container in refrigerator.