Sweet Onion Potatoes au Gratin

The picture doesn't really do this justice.  It was really delicious.  We used fingerling potatoes, so that's why it looks pink/purple--because it is.  You can't see the caramelized onions (which are delicious) because they're hidden under that layer of cheese (yes please).  Tell me--what's not to love here?  So don't judge the recipe by the picture; try it yourself.  It's easy enough to make on a weeknight but decadent enough to serve for a special occasion.  You'll love it.  (I adapted this recipe from Rachael Ray's.)

Sweet Onion Potatoes au Gratin

2 Tbsp butter
1 large sweet onion, thinly sliced
Salt and pepper
1 bay leaf
2 pounds fingerling potatoes (or Baby Yukon Golds)
1/3 - 1/2 cup half and half
1/4 - 1/2 cup Parmesan cheese
8 oz Swiss cheese

Heat a small skillet with the butter over medium heat. Add the onions, season with salt and the bay leaf, and cook until very soft and sweet and lightly caramelized, 20 minutes. Season with salt and pepper, to taste, and discard the bay leaf.

While the onions cook, put the potatoes in a medium size pot and cover with water. Bring to a boil, then salt the water and cook until tender, 12-15 minutes. Drain and return the potatoes to the hot pot. Mash the potatoes with the half and half and Paremesan cheese.  Season with salt and pepper to taste.
 Preheat the broiler.  Arrange the mashed potatoes in a shallow casserole dish (I used 8"x8"). Top the potatoes with the onions and Swiss cheese. Place the dish under a hot broiler until bubbly, about 2 minutes. Remove from the oven and serve hot.