Preheat oven to 375°F.
Add sweet potatoes and Yukon gold potatoes to a roasting pan and rub olive oil over them. Season with allspice, salt and pepper. Bake until potatoes are tender, about 50 minutes to 1 hour.
While the potatoes are roasting, start the meat filling by melting the butter in a pan over medium heat. Add the pork, turkey, shallots and garlic and sauté until the meat is golden, about 5 to 10 minutes. Add the celery, carrots, cinnamon and cloves and sauté over high heat until carrots soften, about 5 minutes.
Sprinkle with flour and cook for 2 to 3 minutes. Deglaze the pan with the white wine and cook for 2 minutes. Add the Worcestershire sauce, Dijon mustard, thyme, savoury, rosemary and chicken stock. Bring to a boil then reduce to low heat. Season to taste with salt and pepper. Simmer covered until all the moisture is absorbed by the meat, about 20 minutes. Remove from the heat and set aside.
Add peas to the meat and gently mix inches Transfer the meat filling to a baking dish (about 7½" X 11½" X 3" deep).
Peel potatoes and gently mash them in a bowl. Add butter, cream, nutmeg and salt and pepper and stir until blended. Spoon the mashed potatoes onto the meat filling and spread evenly with a spatula to completely cover it.
Bake uncovered at 375°F until golden brown on top and meat filling is bubbling, about 25 to 30 minutes.