• Bring a large pot of salted water to a boil. Cook the pasta shells according to package instructions until al dente. Drain and set aside.

Caramelize the Onions:

• In a large skillet over medium heat, melt 4 tbsp butter. Add the sliced yellow onions and cook, stirring occasionally, for about 20-25 minutes or until the onions are deeply caramelized and golden brown. Remove from the heat and stir in the worcestershire sauce then set aside.

Prepare the French Fried Onion Topping:

• Slice the shallots into thin rings, about 1/4 inch thick.
• Toss the sliced shallots with 2 tbsp flour, 1/2 tsp salt, and 1/2 tsp black pepper until lightly coated.
• In a separate skillet, heat a few tablespoons of oil over medium-high heat. Fry the shallots in batches until golden and crispy. Remove and drain on paper towels.
• In a mixing bowl, combine the fried shallots, panko breadcrumbs, and 1 cup Gruyere. Set aside.

Make the Cheese Sauce:

• In a large saucepan, melt 4 tbsp butter over medium heat. Whisk in the flour and cook for 1-2 minutes to form a roux.
• Gradually whisk in the milk and half and half, cooking until the sauce thickens, about 5 minutes.
• Reduce heat to low and stir in the Gruyere, Gouda, Swiss, and Parmesan cheese. Season with garlic powder, salt, black pepper, and dried thyme, stirring until smooth and creamy.

Combine and Bake:

• Preheat the oven to 375 F.
• In a large baking dish, combine the cooked pasta, cheese sauce, and caramelized onions. Mix until evenly combined.
• Pour the mac and cheese into a greased baking dish, spreading it into an even layer. Sprinkle the French fried onion topping evenly over the mac and cheese.
• Bake for 15 minutes just until the top is golden and the cheese has melted.
• Remove from the oven and garnish with fresh thyme if desired, serve and enjoy!