Check the mussels over carefully for cracked shells and discard any that refuse to close when tapped firmly. Put in a deep saucepan with the wine or vermouth.
Bring to the boil, covered tightly with a lid, and let them cook for 2-3 minutes until their shells have opened. Remove from the heat, cool slightly and pull the mussels from their shells. Reserve the cooking liquid.
Roll up the cabbage leaves and shred into pappardelle thick ribbons. Melt the butter in a shallow pan over a moderate heat and add the olive oil. Add the garlic and cook for a couple of minutes.
Add the crushed juniper berries and the cabbage. Fry for a couple of minutes until the cabbage is bright green and starting to soften. Cover with a lid and continue cooking for 3 minutes.
Remove the cabbage and set aside . Pour in the reserved mussel cooking liquor and bring to the boil then add the double cream and a little pepper. Shake back and forth until you have a creamy sauce.
Return the cabbage and mussels briefly to the pan, then serve immediately.