To make the burgers, combine the ground beef/mince, garlic, breadcrumbs, egg, herbs, salt and pepper and mix well.
Form 8 patties and place on a plate/tray. Cover with clingfilm and place in the fridge to rest.
To make the basting sauce, combine all the ingredients in a small saucepan and allow to come to a boil. Turn down the heat and allow to simmer gently for 5 minutes then remove from the heat and allow to cool.
To make the caramelized onions, fry the onions in the olive oil over medium heat until they start to soften and turn golden (approximately 15 minutes). Add the sugar and Balsamic and cook for another 10 minutes, stirring regularly to prevent the onions from burning. Remove from the heat and set aside.
To cook the burgers, preheat an outdoor grill or grill pan over medium-high heat. If using an outdoor grill, the fire needs to be medium hot to create a crust on the outside of the burgers without burning the basting sauce.
Cook the burgers for 2 minutes per side then start basting with the Bourbon sauce. Cook to your preference. Toast the sesame buns while the burgers are cooking.
To assemble the burgers, top the buns with the lettuce, tomato, the basted patties, cheese and a generous spoonful of caramelised onions.