Note: you will have extra Demi Glace left for dipping fries or making more burgers.
Easy Red Wine Demi Glace:
In a small pot, combine stock and red wine, bring to boil over medium-high heat. Lower the heat to medium and add sliced shallots, bay leaf, thyme, salt and peppercorns. Simmer for 45-55 minutes until reduced in a little more than half, stirring occasionally. Stir soft butter and flour into paste and add it to the sauce. Slowly stir until thickened. Set aside.
Caramelized Onions:
Preheat frying pan with olive oil on medium heat. Add sliced onions and sprinkle with a little bit of sugar and some salt. Stir well. Cook slowly (medium to medium-low heat), stirring often, as the onions caramelize to nice brown color. Set aside when done.
Burgers:
Mix buffalo meat, onion, bread crumbs, salt and pepper until all evenly combined. Divide into two patties and cook over medium heat until reached desired temperature.
Add slices of Monterrey Jack cheese on top to let the cheese melt.
Assemble burgers by spreading some Demi Glace on the bottom bun and adding burger patties with cheese, caramelized onions and some more sauce on top.