Divide white cake batter into two portions. Colour one portion with red gel food colouring. Scoop red batter into cupcake liners, then carefully top with white batter. Bake as per recipe directions. Using a large round tip, pipe a white icing swirl on top of cupcake. Dip icing peak halfway into red glaze icing, letting excess drip off. Set on a rack until glaze firms.