2 tablespoons olive oil, divided
½ teaspoon sugar
1 yellow onion, thinly sliced
4 cremini mushrooms, finely chopped
8 to 10 chard leaves, stems removed and leaves finely chopped
½ teaspoon kosher salt
3 tablespoon soften butter
8 slices grainy bread
2 tablespoons Dijon mustard
2 cups grated Gruyère cheese
Place two large rimmed baking sheets inside the oven and preheat to 425°F.
In a large skillet over medium-high heat, melt 1 tablespoon of oil and stir in the sugar until it dissolves. Add the onion and cook, stirring frequently, until tender and translucent, about 10 minutes. Scrape up any browned bits in the skillet with a spatula and mix them back in with the onion.
Push the onions aside and add the remaining 1-tablespoon of oil. Add the mushrooms, chard, and salt. Cook until the vegetables are tender and wilted, about 5 minutes. Keep stirring them around to let any excel liquid cook off.
To assemble the sandwiched, thoroughly butter all the bread on one side. Turn half the slices over, buttered side down, and spread the mustard over them. Layer equal amounts of the cheese, onion, mushrooms, and chard on each slice, then top with the remaining slices of bread, buttered sides up.
Transfer the sandwiches to the hot baking sheet in the center of the over and place the other hot baking sheet on top, pressing down slightly, bake for 6 to 8 minutes until the bread is toasted on the outside and the cheese is melted on the inside.
Source: Ly, Linda. “Leafy Greens.” The CSA Cookbook: No-waste Recipes for Cooking Your Way through a Community Supported Agriculture Box, Farmers’ Market, or Backyard Bounty. Minneapolis, MN: Voyageur, 2015. 57-87. Print.