Start by slicing a white onion (1 large) into thin slices. Add butter (2tbsp) to a skillet and heat over medium heat. Lay the onions to the HOT pan and cook gently until slightly browned. Add the brown sugar (¼ cup), salt (1 tsp) and black pepper (1 tsp). Stir the mixture and cook until syrupy and the onions have softened. Add the coffee (1 cup) and then cook until the coffee has evaporated, stirring often, and the onions are completely soft. Set these aside.

Make the chimichurri by chopping the parsley (1 head), mincing the garlic cloves (3) and dicing the red bell pepper (2 tbsp). Combine these ingredients in a bowl with olive oil (½ cup), red wine vinegar (2 tbsp), dried oregano (1 tsp), kosher salt (1 tsp), red chili flakes (1 tsp), and black pepper (½ tsp). Set this mixture in the refrigerator until the burger is done.

Form the burgers into 1 inch thick round patties. 8 ounces each. Next, liberally season the burgers all over with Kosher salt (1 tsp) and black pepper (1 tsp). Heat the frying pan to 375 degrees and lay the burgers down into the pan. Cook the burgers on 1 side for 3 minutes and then flip the burgers over. Add the butter (2 tbsp) to the pan with garlic cloves (2) and the sprig of rosemary. Let the garlic and rosemary cook in the melted butter. Start spooning the sauce over the tops of the burgers. Cook the burger another 3 minutes. Remove the pan from the heat, lightly cover the burgers with foil and let the burgers rest for 5 minutes.

Slice the Kaiser rolls in half and lightly toast the buns. Spread the bottom half of the bun with the stone ground mustard aioli (2 tbsp). Check the temperature of the burgers and remove the burgers from the pans (140 degrees F) and slide them onto the bun. Top the burger with the caramelized onions and the pepper jack cheese. Melt the cheese and then add the chimichurri sauce.

Close the burger with the top bun, pressing lightly to help secure all the ingredients.