Whenever I make grilled cheese, I always add caramelized onions, mushrooms, and whatever greens I have on hand. This recipe is also great in that all your sammies are done at the same time, without the first getting cold by the time the last ones are done. I wish you could see the mouthwatering picture of these morsels. Adapted from The CSA Cookbook by Linda Ly.
Place two large rimmed baking sheets inside the oven and preheat to 425F. If your baking sheets cannot fit side by side, place on sheet on the center rack and another sheet on whichever rack remains.
In a large skillet over medium-high heat, melt 1 Tbsp of oil and get up to heat.
Add the onion and cook, stirring frequently, until tender and translucent, about 10 minutes.
Add the other Tbsp of oil, the mushrooms, sugarloaf, and salt. Cook until the vegetables are tender and wilted, about five minutes. Keep stirring them around to let any excess liquid cook off.
To assemble the sandwiches, thoroughly butter all the bread on one side. Turn half the slices over, buttered side down, and spread mustard over them. Layer equal amounts of the cheese and veggie sauté 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 oven and place the other hot baking sheet on top, pressing down lightly. Bake for 6-8 minutes until the bread is toasted on the outside and the cheese is melted on the inside.