In most cheesecake recipes I have read the butter is melted for the crumb base. In NIgella's Nutella Cheesecake recipe it lists softened butter. Does this mean the butter is softened as if making a cake mixture?
Nigella's Nutella Cheesecake has a base made from digestive biscuit (graham cracker) crumbs that is bound with softened butter and a little Nutella. As the base is made in a food processor it is fairly easy to get the soft butter to blend with the crumbs, as well as saving having to wash up a saucepan. The butter should be quite soft (room temperature). It does not need to be beaten or creamed first.
Quite often melted butter is used in crumb bases and if you make the base without a food processor you may find it easier to incorporate the butter if you melt the butter first, though you will still need to mix in the Nutella as we don't recommend melting the Nutella.