Onion Potato Gratin

What we're cooking for Christmas dinner:

• 3 lbs Yukon gold potatos, peeled and cut into 1/4" rounds
• 1 & 1/2 lbs yellow onion, sliced into thin rings
• 2 cups grated and packed Gruyere
• 4 oz. grated and packed Parmesan
• 1 & 1/3 cup heavy cream

1. Put onions and potatos into a large suace pana nd cover with water (you may need two pans)
2. Bring to boil, simmer 3 minutes, drain.
3. Arrange half of potatoe and onion mixture in lasagne pan (11X14) .
4. Cover with @ 1/3 of cheeses
5. Put reamining potato and onion mixture on top of cheese layer.
6. Pour cream over mixture and add salt and pepper to taste.
7. Top with remaining cheese.
8. Bake uncovered at 400 F. about 25 minutes until thickened.
   
9. Broil until golden on top to finish.

This is originally from Bon Appetite.