Stir the egg yolks and eggs well with the sugar until the sugar dissolves (avoid foaming as much as possible). Grate the oranges with the sugar cubes.
Mix whipping cream and milk, heat until just before boiling, let orange sugar cubes melt in it. Add the liqueur and chill the orange milk (in an ice water bath). Then mix into the egg mixture.
Pour the flan mixture into portion molds, cover them with aluminum foil and place them in a hot water bath. Cook in a heated stove at 200 degrees for about 45 minutes. Cool, put in a cool place until serving.
For the mint sauce, bring the cream together with the milk to a boil, pour in the plucked mint leaves and steep for about ten minutes. Then strain through a sieve.
Beat the egg yolks with the sugar until creamy. Then add the hot flavored milk, stirring continuously. Continue stirring on the stove over a mild temperature until the cream thickens. Finally, add the peppermint liqueur and stir the sauce until cold.
Turn flans out onto dessert plates. Pour over the peppermint sauce and garnish with a few peppermint leaves, if desired.