While burgers cook, halve buns and place on a baking sheet. Toast in oven until golden brown, 2-3 minutes. Once garlic is done roasting, mash with a fork until smooth. In a small bowl, combine ½ TBSP mayonnaise (you’ll be using more later), remaining balsamic vinegar, a large drizzle of oil, and as much garlic as you like. Season with salt and pepper.