Before starting, remove 1 tbsp butter (dbl for 4 ppl) from the fridge and set aside to come up to room temperature. Preheat your broiler to high. Wash and dry all produce. Peel, then thinly slice onion. Heat a medium pot over medium heat. When hot, add 1/2 tbsp butter (dbl for 4 ppl), then onions. Cook, stirring occasionally, until golden-brown, 5-7 min. Add half the balsamic glaze and season with salt and pepper. Cook, stirring occasionally, until onions are dark golden-brown, 2-3 min. Transfer onions to a plate. Carefully wipe the pan clean.

While onions caramelize, core, then cut pear into 1/4-inch slices. Halve tomatoes. Halve rolls. Whisk remaining balsamic glaze with 1/2 tbsp oil (dbl for 4 ppl) in a large bowl. Season with salt and pepper. Cut brie into 1/4-inch slices.

Heat the same pan (from step 1) over medium-high. When hot, add 1/2 tbsp butter (dbl for 4 ppl), then swirl to melt. (NOTE: Do not use the softened butter in this step, save it for step 4) Add pears, then sprinkle with 1/4 tsp sugar (dbl for 4 ppl). Cook cut pears, stirring occasionally, until tender-crisp, 1-2 min. Transfer pears to a plate to cool.

Arrange bottom rolls on a foil-lined baking sheet, cut-side up. Broil in the top of the oven until golden-brown, 1-2 min. (TIP: Keep an eye on rolls so they don't burn!) While bottom rolls toast, spread softened butter on top rolls.

Spread Dijon on toasted bottom buns, then top with pears and caramelized onions, then brie. Arrange assembled rolls and buttered rolls, cut-side up, on the same foil-lined baking sheet. Broil in the middle of the oven until brie is warm and top rolls are golden-brown, 3-5 min. (TIP: If you want meltier brie, remove the top rolls once they're golden-brown and continue broiling the bottom rolls until desired doneness.)

Add spinach and tomatoes to the bowl with vinaigrette. Toss to combine. Place top rolls on assembled melts, then cut in half crosswise, if desired. Divide melts and salad between plates. Sprinkle salad topping mix over salad.