Preheat the oven to 180°C.
Season the pigeon crowns and rub with butter and mace, then let rest for 30 minutes.
Sear the crowns in a hot ovenproof pan with oil until brown.
Roast at 180°C for 12 to 15 minutes, then rest in a warm place for 5 minutes.
Sauté shallots in the pan after removing excess fat.
Add vinegars and reduce by half over heat.
Add stock and reduce by one-third.
Whisk in butter and season to taste.
Carve the pigeon breasts off the bone.
Strain the sauce and use half to glaze the breasts.
Stir parsley and chervil into the remaining sauce.
Increase oven temperature to 200°C.
Toss potato slices in clarified butter and seasoning.
Layer potatoes in small pans and roast for 10 to 15 minutes until golden.
Blanch spring onions in boiling water for one minute, then refresh in ice water.
Warm peas and onions in a frying pan with butter for two minutes.
Serve the pigeon on the potato cakes topped with vegetables and drizzled sauce.