This easy gratin is a great weekend brunch option. From Williams-Sonoma Cooking at Home.
*Makes 4–6 servings
4 tablespoons (2 oz.) unsalted butter
1 shallot, minced
6 oz. cremini mushrooms, sliced
1 1/2 teaspoons dry mustard
2 tablespoons red wine vinegar
1 small bunch Swiss chard, about 6 oz., coarsely chopped
1 bunch spinach, about 3/4 lb., tough stems removed and coarsely chopped
Salt and ground pepper
1/3 cup (1 1/2 oz.) fine dried bread crumbs
3–4 tablespoons grated Parmesan cheese
1 tablespoon olive oil
Preheat the oven to 325°F. Lightly butter a shallow 1-qt baking dish.
In a large frying pan over medium heat, melt 2 tablespoons of the butter. Add the shallot and mushrooms and sauté until softened, about 2 minutes. Stir in the mustard and sauté for 10 seconds longer. Stir in 1/2 cup (4 fl. oz.) water and the vinegar. Add the chard and spinach, a handful at a time, waiting for each handful to wilt before adding the next one. It should take about 30 seconds for each addition to wilt. When all of the greens have been added, season with salt and pepper and remove from the heat.
Transfer to the prepared baking dish. Sprinkle the breadcrumbs and cheese evenly over the top, and then drizzle evenly with the oil. Cut the remaining 2 tablespoons butter into small pieces and dot the top.
Bake until the gratin is heated through and the top is golden brown, 15–20 minutes. Serve right away, directly from the dish.