Onion Base:

3 large yellow onions, thinly sliced

3 tbsp butter

2 cloves garlic, minced

1 tsp dried thyme

Salt and freshly ground black pepper, to taste

Cheese Sauce:

3 tbsp all-purpose flour

4 cups beef broth (or vegetable broth for vegetarian)

1 cup half-and-half or heavy cream

1 ½ cups grated Gruyère cheese

1 cup sharp white cheddar cheese, grated

Pasta & Topping:

12 oz elbow macaroni

½ cup extra grated cheese for topping

French bread or baguette slices, toasted (optional)

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In a large skillet over low heat, melt butter and add sliced onions. Cook slowly for 30–40 minutes, stirring occasionally until onions are deeply caramelized and golden brown.
Add garlic and thyme, then season with salt and pepper. Stir and cook 2 more minutes.
Sprinkle flour over the onions and stir to coat evenly. Gradually whisk in broth, then add half-and-half or cream. Stir constantly until the sauce thickens slightly.
Remove from heat and stir in Gruyère and sharp white cheddar until smooth and melted.
Meanwhile, cook macaroni according to package directions until al dente. Drain, reserving ½ cup of pasta water.
Fold the cooked pasta into the cheese-onion sauce until evenly coated. Add a splash of reserved pasta water if needed to loosen the sauce.
Transfer to an oven-safe dish, top with extra cheese, and arrange toasted baguette slices on top if using.
Broil for 2–4 minutes until the cheese bubbles and turns golden brown. Serve hot.

Use vegetable broth for a vegetarian version.

Grate cheese fresh for the smoothest sauce texture.

Cook onions low and slow for the best caramelization.

Add a touch of sherry or white wine to the onions for extra depth.

Top with garlic croutons instead of baguette slices for crunch.