Line jelly-roll (11 x 15-inch) baking pan with foil, and spray with vegetable cooking spray. Prepare mix, following directions for cakelike brownies; bake in jelly-roll pan for 30 minutes.
Once brownies are completely cooled, cut into squares, three rows lengthwise by five rows crosswise. Cut squares in half diagonally. Remove packaging from ice cream, and cut into 1/2-inch-thick slices. Cut triangles of ice cream to fit brownies. Sandwich together and serve.