Peel, cut, and boil the potatoes for 15-20 minutes or until tender. Mash potatoes with some of the boiling water, adding butter, milk, salt, and pepper to taste. Set aside
Finely chop shallots, onion, and garlic. Sauté garlic, onion, shallots, and meats separate on the same pan. Discarding liquids each time, placing the sautéed ones on the bottom of the baking dish you are using.
To assemble the casserole, mix well all the meats, garlic, onion, and shallots until well combined, taste and rectify seasoning if needed. Spread all over the bottom of the dish.
Then layer mashed potatoes on top of the meats layer. Each layer should be about the same height. Heat oven to 200 C and cook uncovered for 30-35 minutes or until the top of the casserole is golden brown.