Drain the plums on a sieve. Collect the juice. Mix starch and 3-4 tablespoons of juice. Put the rest of the juice, lemon zest, juice, almond liqueur, sugar and cinnamon stick into a pot and bring to the boil. Remove from heat and thicken with the mixed starch.
Bring to the boil again. Add plums and fold in. Let cool down. Arrange the ice cream and plum compote in glass bowls and serve after having been left to stand, sprinkled with almond flakes and decorated with lemon balm