This French Onion Soup Mac & Cheese is the ultimate marriage of two comfort food classics. It starts with deeply caramelized onions, slow-cooked for rich flavor, then transitions into a creamy, savory cheese sauce made with a touch of beef broth, milk, and heavy cream. Blended with Gruyère, cheddar, and Swiss cheeses, the result is a luxurious, melty dish topped with broiled cheese for a golden finish. It’s cozy, decadent, and utterly irresistible.