4 lg Idaho potatoes
2 lg Garlic heads, roasted
2 lg Onions, baked
1 1/4 c  Heavy cream
Salt and pepper to taste
1 c  Gruyere

Remove the papery covering of the garlic heads, but do not peel and do not
separate the cloves. Wrap well in foil and put them in the oven. Put the
onions on a double sheet of foil, but do not wrap them; put them in the
oven. Pierce the potatoes in several places with a thin skewer or the tines
of a fork. Put them directly on the oven rack. Bake the garlic for one
hour and the onions and the potatoes for an hour and a half at 425. After
an hour pull out the garlic heads, unwrap, and let cool for 5 minutes.
Separate the cloves and squeeze them over a bowl so the softened garlic
pops out into the bowl. After 1 1/4 hours, pull out the onions and
potatoes. If the onions are not very soft (almost collapsed) put them back
in for a few minutes. Perforate the potatoes lengthwise and crosswise with
the tines of a fork and squeeze. Scoop the potato flesh into a bowl and
mash it with a potato masher. With a sharp knife, cut off the stem and root
ends of the onions. Remove the skin and the first layer. Put the onions in
a food processor and puree. Combine the potatoes, garlic, onion, 1/4 cup of
cream, and salt and pepper in the bowl of a mixer. Beat (with the paddle
blade) until smooth and blended, then scrape the mixture into a large
gratin bowl. Sprinkle the top with cheese. (The recipe can be made ahead
to this point and kept in the refrigerator, covered, for a day or so. Bring
to room temperature before proceeding.) Reduce the oven temperature to 350.
Pour the remaining cream over the mixture. Bake, uncovered, for 40 – 50
minutes, or until the top is browned and bubbly and the cream has cooked
down to a very thick suace-like consistency. Try to arrange to have some
leftovers; this is very good when it is cold.