Take the butter out of the fridge, bringing to room temperature. Preheat the oven to 200 degrees. Halve, peel, and thinly slice the onions. Heat a drizzle of oil in a large pan over medium heat. Add the sliced onions and cook, tossing, until slightly caramelized for 8-10 minutes. Stir in 2 Tablespoons balsamic vinegar and cook for another until jammy. Remove from the pan and set aside.

While the onions cook, core and thinly slice the pears. Tear the lettuce into large bite-sized pieces, discarding the core.

Spread two slices of bread with 1 teaspoon butter each. On a cutting board, lay the slices butter- side down. Top one slice with 1/4 of the caramelized onions, 1/2 cup gruyere, and pear slices (reserving some for the salad). Spread the other slice of bread with 1/2 teaspoon Dijon mustard. Place it on top of the other slice, butter-side up. Repeat this process for the remaining sandwiches.

Wash out the pan you used for the onions and heat it over medium-low. Working in batches, place the sandwiches in the pan and cook, for 3-5 minutes per side, until golden brown and the gruyere has melted. Place the finished sandwiches in the oven to keep warm until the entire meal is ready.

Make the dressing: While the sandwiches cook, whisk together 2 teaspoons Dijon mustard, the remaining balsamic vinegar, and a drizzle of olive oil in a large bowl. Season with salt and pepper.

Cut the sandwiches in half. Toss the lettuce and remaining pear slices with enough dressing to coat. Season to taste with salt and pepper. Serve the pear salad alongside the grilled cheese sandwiches and enjoy!