Wash the mint and dab dry. Put apple juice into a pot, add jam sugar and bring to the boil while stirring constantly. Let it boil again while stirring for 2 minutes. Remove from the heat, stir in peppermint liqueur.
Fill mint jelly hot and brimful into the prepared glasses. Put the mint stems into the jelly and close the jars. Makes about 3 glasses of 250 ml each.