Pull the orange zest out of the peel (or rub it, but then the liqueur will be a little cloudy).
Put the grain and gin together with the zest (or the abrasion) in a dark bottle (wine bottle works well, but make sure that you choose a liter bottle).
Put the bottle with the mixture in a cool cupboard.
Halve the grated oranges, place in a bowl and cover completely with the mixed sugar. Cover the bowl and let stand for at least 2 days.
Meanwhile, a sweet syrup forms at the bottom of the bowl, which tastes intensely of oranges.
Strain the bottle with the grain-gin-orange pulp mixture, sweeten with the syrup obtained. If you like, you can of course add the orange sugar until the desired sweetness is achieved.