How do you make double cream thick?

Are you whipping it and it's not keeping?

To properly whip up thick cream, whip it cold in a chilled bowl. Then let it set in the refrigerator an hour or so, this will separate out any liquid milk in the cream. Skim the cream off this and whip it again in a clean chilled bowl with a little vanilla and powdered sugar. This should stay stiff and thick.