For the mint jelly, wash the mint leaves, pour 1/8 l of boiling water over them and steep for about 15 minutes. Drain.
Mix the extract with the cider, lemon juice and jelling sugar, bring to a boil and boil for 4 minutes until bubbly.
Remove pot from heat, mix in liqueur and pour hot into twist off jars. Immediately seal and turn jars upside down for a few minutes.