Potato Gratin with Sauteed Onions

I made a potato and summer squash gratin a few months ago, but it wasn't exactly traditional - there was no milk. This time, I wanted to do a classic version, with some sauteed onions for extra flavor. I used two percent milk instead of cream, whole milk or half and half, but if you want a heavier (and, yes, even more traditional) gratin, use the good stuff. Even with the lighter milk, though, this gratin was super creamy and cheesy. The top layer gets golden brown and crispy, which offers a nice contrast in texture. We ate this as a main course - it was that good - but it would go well as a side, too. Relied on this recipe, with some tweaks.



Total time to cook: 1.5 hours

Ingredients:
3 medium white potatoes, peeled and sliced very thin
1 cup sliced white onions
2 tbsp margarine
3/4 cup grated parmesean cheese
Kosher salt
Black Pepper
1.5 cups milk (at least 2 percent, if not heavier)

Steps:
- Preheat the oven to 350 degrees and grease a 7x11 pan with one tablespoon of margarine.
- In a small pan, melt half of a tablespoon of margarine over medium heat. Add the onions and sautee until they start to brown. Turn off the heat.

- Cover the bottom with potato slices, arranging them in slightly overlapping rows. Season with a little salt and pepper and a third of the onions. Sprinkle a third of the cheese evenly over the potatoes and onions.

- Repeat the last step two more times (there should be enough for three layers). Add pieces of the remaining margarine all over the top. Pour the milk slowly over the potatoes, it should come up to the top layer but not go over it. Try to make sure the milk doesn't wash the cheese, onions or seasoning off of the top layers.
- Bake for one hour. At the third-minute mark, take the gratin out and press down on the top layer with a spatula to get some of the milk to cover the top (it'll stay moist that way).
- The gratin is done when the top is golden brown and most of the milk is absorbed. Serve hot.