Put the garlic and olive oil in a heavy saucepan over lowest possible heat and simmer until soft; 30 to 40 minutes.

Drain off oil (reserve for marinades or vinaigrettes).

Purée garlic; set aside.

Meanwhile, prick potatoes with a fork and bake in a 400°F oven for 1 hour, or until soft. While still hot, peel and mash, or pass through a potato ricer.

Melt butter in heavy cream; whisk in puréed garlic.

Stir into potatoes.

Stir in cheeses and season with salt and pepper.

Spoon into a gratin dish.

Place in a 400°F oven for 12 to 15 minutes or until browned and bubbling.