Place 3/4 of the Nutella jar without the lid in boiling water until the cream is very soft and comes out of the jar almost runny.
In the meantime, heat the cream with the condensed milk in a saucepan, but do not boil it. Add the Nutella and stir well over a moderate heat until everything is nice and smooth. Then take the pot off the stove and add the double grain or the vodka, stir well and fill into suitable bottles.
Keep in the refrigerator until you eat it and best enjoy in a chocolate mug!