Salt and pepper roulades, brush each with 1 tsp mustard and sprinkle with crushed tarragon. Roll up 1 cut leek stick and fix roulades with clips, needles or yarn. Sear in hot clarified butter on all sides.
Cut the rest of the leek into small pieces, sauté together with rosemary and garlic and extinguish with broth. Stew for 2 hours.
Remove roulades and keep warm. Strain sauce, squeeze vegetables well and discard. Mix sauce with creme fraiche and tomato paste, bring to a boil and reduce slightly. Serve with boiled potatoes. Carrots and broccoli are recommended as vegetables.