After pressing the bars into an even layer, place them in the freezer for 10 minutes.
Meanwhile, melt 4 ounces of semi-sweet or dark chocolate in a small bowl in 20 second burst in the microwave, stirring after each, until melted.
Pour the melted chocolate over the bars and tilt the pan so that the chocolate covers the bars completely.
Place in the freezer for an additional 20 minutes before slicing.