COMBINE mustard seeds and sherry vinegar in a saucepan. Bring to a boil and remove from heat.

CLEAN belly of all sinew and excess fat; it should be nice and smooth. Aggressively salt and pepper it. Let it sit at room temperature until it starts weeping, about 20 to 25 minutes.

PREHEAT oven to 300℉. Cut oranges and lemons in ½ inch slices and reserve.

PLACE belly, skin-side up, in an oven safe pan just barely big enough for it. Add enough olive oil to cover it by ½ inch and the citrus. Place in oven uncovered and cook for about 3 hours or until tender. (The citrus will caramelize and turn brown. That’s okay.) Remove belly from the oil and let it rest, for about 30 minutes. Then, place in another shallow pan, skin-side up, and crank the oven up to 500℉. Cook the belly in the oven until the skin starts to blister and become crisp, about 10 to 15 minutes longer. Remove from oven, let it cool a little, and cut into portion sizes.

SAUTÉ the greens in olive oil over high heat until they wilt, about 1 to 2 minutes, remove from heat, and add a spoonful of the mustard and sherry mix. Plate the greens, place a piece of belly (best if warm, not super hot) on top, and drizzle with the mustard-sherry mix. Grate zest of lemon on top to garnish.