Heat a large skillet pan for a few minutes so it gets very hot. Add the sunflower oil and sear the lamb racks on both sides but not the ends, until they are browned.
Place the lamb in a roasting tin and drizzle with the olive oil. Sprinkle with the fennel seeds and the garlic. Pour the water around the meat and cover the roasting tin tightly with aluminium foil.
Slow roast in the centre of the oven for 2-3 hours, depending on the size and thickness of your lamb racks.
Transfer the lamb to a serving platter and let stand, covered, for 10 minutes. Deglaze the roasting tin with the cognac, scraping up any delicious bits stuck to the bottom.
Add the wholegrain mustard and remove the pan from the heat. Stir in the double cream and gently reheat until warmed through. Stir through the tarragon and season well to taste.
To serve, spoon a small circle of mustard sauce in the centre of a plate. Top with the freshly cooked gnocchi and arrange a few sliced lamb chops on the side. Garnish with pomegranate seeds, walnut halves, cress leaves and a small piece of salad.
For a quick and easy version, simply fry 8-12 lamb chops in the sunflower oil in a skillet. Deglaze with the cognac and add 50 ml lamb stock before adding the rest of the sauce ingredients.
Alternatively, roast the lamb at 350 °F/180 °C/ Gas Mark 4 for 20 - 25 minutes instead for medium-rare doneness. You might need to cover with foil after 15 minutes to stop browning. Use a meat thermometer to check that the temperature is correct: 145 °F/ 62 °C (medium rare), 160 °F/ 71 °C (medium), or 170 °F/ 77 °C (well done).
Mum of three, daydream adventurer, OU Life Sciences graduate, occasional crafter, ex-pat Canadian & quite possibly Britain's most northerly food blogger.