Before starting, preheat oven to 450˚F. Remove 1 tbsp butter (dbl for 4 ppl) from the fridge and set aside to come up to room temperature. Wash and dry all produce. Garlic Guide for Step 3 (dbl for 4 ppl): 1/8 tsp mild, 1/4 tsp medium and 1/2 tsp extra! Cut potatoes into 1/2-inch wedges.Add potatoes and 1 tbsp oil to an unlined baking sheet. (NOTE: For 4 ppl, use 2 baking sheets, with 1 tbsp oil per sheet.) Season with salt and pepper, then toss to coat. Roast in the middle of the oven, flipping halfway through, until tender and golden-brown, 24-26 min. (NOTE: For 4 ppl, roast in the middle and bottom of the oven, rotating sheets halfway through.)

Meanwhile, heat a medium pot over medium heat. While the pot heats, peel, then cut onion into 1/4-inch slices.When the pot is hot, add 1/2 tbsp (1 tbsp) butter, then swirl the pot until melted. (NOTE: Save softened butter for step 4.)Add onions. Cook, stirring occasionally, until softened, 6-8 min. Add half the balsamic glaze and 1 tbsp (2 tbsp) water, then season with salt. Cook, stirring occasionally, until onions are dark golden-brown, 4-5 min. Remove the pot from the heat.

Meanwhile, peel, then mince or grate garlic.Halve rolls.Cut mozzarella into 4 equal slices (8 slices for 4 ppl).Cut 2 slices from the thickest part of tomato (4 slices for 4 ppl). Transfer tomato slices to a paper towel-lined plate. Season both sides with salt, then set aside.Cut remaining tomato into 1/2-inch pieces.Add pesto and 1/2 tsp (1 tsp) garlic to a small bowl. (NOTE: Reference garlic guide.) Season with salt and pepper, to taste, then stir to combine. Set aside.Add remaining balsamic glaze and 1 tbsp (2 tbsp) oil to a large bowl. Season with salt and pepper, to taste, then whisk to combine.

When potato wedges are almost done, arrange rolls on another unlined baking sheet, cut-side up. Spread 1 tbsp (2 tbsp) softened butter on cut sides, then season with pepper.Toast rolls in the top of the oven until lightly golden, 4-5 min. (TIP: Keep an eye on rolls so they don't burn!)Transfer top rolls to a plate, leaving bottom rolls on the baking sheet.

When potato wedges are done, remove the baking sheet from the oven, then switch the oven to high broil. Pat tomato slices dry with paper towels.Spread half the garlicky pesto on bottom rolls, then top with tomato slices. Season with salt and pepper. Top with mozzarella. Return assembled bottom rolls to the middle of the oven until mozzarella melts, 3-4 min. (TIP: Keep an eye on rolls so they don't burn!)

Meanwhile, add mayo to the bowl with remaining garlicky pesto, then stir to combine. Add arugula and spinach mix and chopped tomatoes to the bowl with vinaigrette, then toss to coat. Carefully stack caramelized onions, some crispy shallots and some dressed greens on melted mozzarella. Close melts with top rolls. Divide melts, potato wedges and remaining salad between plates. Sprinkle remaining crispy shallots over salad. Serve pesto aioli alongside for dipping.