Chard and Sweet Potato Gratin

This is one of those high-effort but high-reward dishes.  It's definitely got a heck of a lot of steps - cooking the chard and then squeezing it dry, making a sauce, slicing sweet potatoes, grating cheese, and then putting everything together and baking.  So it's for sure more of a weekend project rather than a weekday dinner.  That said, if you have the time, this dish is totally worth it.  The creamy potatoes combine really well with the more earthy greens, and the sauce binds everything together nicely.  I'd actually add more cheese and sauce if I made this again - I was adjusting the recipe for the amount of sweet potatoes and chard that we got in our CSA, and I think I got the ratio a little off.  The gratin was plenty creamy and delicious, but hey - you can never go wrong with more cheese and bechamel!  Serve this with a simple protein - maybe roasted chicken or seared steak - and you've got a fantastic dinner.

Chard and Sweet Potato Gratin (adapted from Smitten Kitchen, original recipe here)
Serves 6 as a side dish

2 T unsalted butter, divided
1/2 small onion, minced
2 bunches Swiss chard (about 1-1/2 pounds)
A few grates of nutmeg
Salt and pepper
1 cup half-and-half, plus a little extra as needed
1 garlic clove, minced
1 T flour
1 pound sweet potatoes, peeled and cut into 1/8-inch thick rounds (a food processor is great for this)
1 T minced parsley
1-1/2 tsp minced fresh oregano
2-1/2 ounces Emmentaler cheese, grated

1. Prepare the greens.  Melt 1 T of the butter in a heavy pot over medium-low heat, stirring often, until softened and starting to brown.  While the onions cook, separate the chard leaves from the stems.  Chop the stems into fairly small pieces, and cut or tear the leaves into roughly 1-inch pieces (nothing here has to be exact).  Once the onions are soft, add the chard stems along with the nutmeg and a sprinkle of salt and pepper.  Cook, stirring, until the veggies are tender, about 8 minutes.  Increase heat to medium-high and add the chard leaves in batches if necessary, stirring until all the greens are wilted.
2. Line a colander with cheesecloth and pour the greens into the cheesecloth.  Let rest until cool enough to handle, and then squeeze the greens to remove as much liquid as possible - it will be a lot!  Set aside.
3. Make the sauce.  Combine the half-and-half and garlic in a small saucepan and bring to a simmer.  Meanwhile, melt the remaining 1 T butter in a nonstick skillet over moderate heat.  Add the flour and whisk to combine using a silicone whisk (which will be safe for the nonstick coating).  Cook the roux, whisking, for about 1 minute.  Slowly whisk in the warm half-and-half and boil, whisking, for one minute.  Season with salt and pepper and then set aside.
4. Assemble the gratin.  Preheat the oven to 400 degrees and spray a 1-1/4 quart (or so) baking dish with oil.  Spread half the sweet potatoes into the dish in an even layer.  Sprinkle with a little salt and pepper, a quarter of the herbs, and about 2 T of the shredded cheese.  Distribute half the greens evenly over the cheese, and the season with a bit of salt and pepper, a quarter of the herbs, and 2 T cheese.  Check the bechamel - if it's quite thick, whisk in a little more half-and-half to get a pourable consistency.  Then pour half the bechamel sauce over the greens.  Spread it around a bit with a rubber spatula.  Then repeat the same layering as the first time around, ending with any remaining cheese.
5. Bake about 1 hour, until golden and bubbling.  Let stand 10 minutes before serving.
6. If you want to prepare this ahead - you can prep and assemble everything the day before and stash in the fridge.  Then you'll just have the baking to do the night you want to eat the gratin.