Caramelize the sugar in a medium-sized saucepan and add the peeled, pitted and diced pears, toss so that the caramel covers the pear pieces.
Then deglaze with the pear juice and pear liqueur, add the cinnamon stick and, if you like, the lemon zest, bring to the boil and simmer over medium heat until the juice is reduced and the pear pieces are soft. Remove the cinnamon stick and go through with a pounder until everything is nicely shaped. Pass through a sieve and add the lemon juice to taste.