Jameson Whiskey Blue Cheese Burger with Guinness Cheese Sauce + Crispy Onions

Name: Jameson Whiskey Blue Cheese Burger with Guinness Cheese Sauce + Crispy Onions
Prep time: 30 min
Cook time: 30 min
Total time: 1 h
Cuisine: American
Ingredients: 2 large white onions (halved and then sliced very thin); 2 cups buttermilk; 2 cups flour; 1 tablespoon kosher salt; pinch of pepper + cayenne pepper; oil (for frying); 1/4 cup whiskey; 1/4 cup ketchup; 2 tablespoons soy sauce; 2 tablespoons honey; 1 teaspoon dijon mustard; 1 teaspoon Worcestershire sauce; 1/4 teaspoon cayenne pepper (or to taste); 1/4 teaspoon pepper; 1 1/2 pounds ground beef; 4 ounces blue cheese (cut into 4 cubes); salt and pepper (for sprinkling); 4 good quality buns (toasted); 4 tablespoons unsalted butter; 4 tablespoons flour; 1/2 cup guinness beer; 1/2-1 cup milk; 8 ounces sharp cheddar cheese; salt and pepper (to taste)