Heat the oil in a non-stick pan. Sauté the garlic, mushrooms, and onion until soft, about 3 - 4 minutes. Add the turkey and brown while breaking it up into smaller pieces. Stir in the flour, cook for 2 minutes. Season with salt and pepper. Stir in the broth, ground sage, and thyme. Simmer with a lid until the broth concentrates in flavor and thickens. Taste and adjust the seasoning with salt.
In the meantime, in a pot of salted boiling water boil the potatoes until a fork can easily slide in and out, about 8-10 minutes. Melt the butter in a saucepan over low heat and add the cream to warm. Mash up the potatoes and add in the butter and cream. Whip until smooth. Season with salt and pepper to taste and set aside.
Place the beef mixture into an appropriately sized oven safe dish, spoon the mashed potatoes on top or use a piping bag with a star tip (optional). Place under the broiler until golden brown. Let sit for 2 - 3 minutes before portioning. Serve with bread.