Sauté the shallots with the butter until golden brown. Add the sugar and balsamic vinegar, puree and cool.
Season the meat with salt and pepper, and add the basil and caramelized shallot puree. Form into even 6 oz. portions and chill.
Grill or cook the burgers on a griddle to medium and top with the fresh mozzarella. Transfer the burgers to the buns, add tomato slices, and serve.
These burgers can be created into sliders by reducing the portion size to 2 oz.; a great idea for your next cocktail party