Remove the peel from the oranges and fillet them, remove the peel from the mango fruit and cut the flesh into small pieces. Soak the gelatine in cold water.
Mix the orange juice with the liqueur. Melt the soaked gelatine in hot water in a ladle. Stir the gelatin into the orange juice, pour a small amount of jelly into an oblong mold (e.g. a loaf pan, cover it with plastic wrap) or baking dish and set aside to cool. Stir the rest in iced water until cooled.
When the jelly is firm, spread the orange fillets and mango cubes evenly in the mold and pour the almost solidified orange jelly over them. To turn out, place the mold briefly in hot water, then turn out onto a board and cut into pieces or slices.
Sauce: caramelize the sugar in a small saucepan, extinguish with orange juice and the orange marmalade and lightly bubble until the caramel is dissolved. Cool the sauce and flavor with the liqueur.
Serving suggestion: Arrange 1 slice of orange-mango jelly with 1 scoop of orange ice cream on each of the portion plates dusted with powdered sugar, add a slice of orange (peeled beforehand) and drizzle with the orange sauce.