Form a dough by processing flour and salt with egg whites and 300ml water.
Knead dough for five minutes, shape into a sausage, and chill for 30 minutes.
Preheat the oven to 150°C and season the lamb.
Brown the lamb in a hot frying pan for 5 minutes and then chill.
Blanch sea lettuce in boiling water for one minute and drain.
Mix softened butter with the sea lettuce and set aside.
Roll half the dough to 1cm thickness and top with herbs, butter mixture, and lamb.
Seal the dough around the lamb, brush with egg yolk, and season with salt and pepper.
Bake the wrapped lamb at 150°C for three hours and let it rest.
Increase oven temperature to 180°C.
Roll remaining dough to 1cm thickness and divide into eight pieces.
Wrap potatoes in dough pieces with herbs and sea lettuce butter.
Seal dough, brush with egg yolk, season, and bake for 45 minutes.
Sauté lamb trimmings in butter, deglazing twice with water until evaporated.
Add shallots, garlic, herbs, and fry for five minutes.
Reduce wine by half, add chicken stock, and simmer gently.
Wilt sea beets and spinach in butter for three minutes.
Break open and discard the salt crusts and slice the lamb thinly.
Strain the jus and serve lamb and potatoes over greens garnished with sorrel.