Ask your butcher to de bone the capon for you, preferably by removing the carcass without splitting the meat. Mix the livers, bacon, mortadella, pork, chicken, bread crumbs, onion, cheese, herbs, garlic, pistachios, chestnuts and zest and bind together with the eggs. Season the meat filling and push through the cavity of the capon. Press the filling well and shape the capon to its shape. Truss with a few cocktail sticks, thigh the legs together with some aluminum foil. Season the capon all around. Cook the mirepoix with a spoon of olive oil until browned, add the tomato paste and the stock. Transfer the stock to a deep baking tray and place the capon on top. Drizzle with olive oil and bake for ½ to 2 hours in a moderate oven or until no blood comes out when a skewer is inserted in the thickest part of the bird. Remove the capon from the dish, strain the liquid and thicken slightly if necessary with corn flour to obtain a gravy consistency. Serve the capon sliced with the gravy, root vegetables and new potatoes