Remove the tough central stalk from each leaf of cavolo nero, and cut each leaf into three or four pieces. Blanch in boiling salted water for a few minutes only, until tender and bright green. Drain and dry.
Put the double cream and 5 whole garlic cloves into a pan and simmer until the garlic is soft. Purée in a blender.
In a separate pan, heat the olive oil and fry the remainin