Melt the butter in a pan and brown the garlic and mushrooms. Add the mushrooms to the potatoes with the shallots, basil and half of the gruyère cheese.
Grease 4 tartlets racks and line each of them with 2 filo pastry sheets folded in 2. Fill with the mashed potatoes and mushrooms mix. Sprinkle the leftover cheese on top.
Bake the tartlets for 15 minutes at 180°C (350°F) until brown and serve with a salad.
