Wash the untreated orange and rub dry. Finely grate half of the peel. Then bring to the boil with sugar and 6 tablespoons of water. Leave to cool
Squeeze the untreated orange and so many other oranges until you get 1/2 l juice. Mix the orange, lemon juice and liqueur well with the sugar solution. Pour into a wide, freezable bowl (preferably metal)
Freeze everything for 3-4 hours. As soon as a layer of ice forms on the surface (after about 30 minutes), stir everything vigorously with a whisk. Then stir vigorously about every 30 minutes
Form 4 large scoops from the orange sorbet with an ice-cream scoop if necessary and place in the freezer for another 15 minutes. Arrange the sorbet with kumquat slices and mint