Season and sear the chicken: Pat the chicken dry and season with 1/2 teaspoon of the salt and the pepper. Heat 1 tablespoon of the butter and the olive oil in a large oven-safe skillet over medium-high heat and cook the chicken for 5 to 6 minutes, until browned and cooked to 165°F. Transfer to a plate.

Caramelize the onions: Reduce the heat to medium-low and melt the remaining 2 tablespoons of butter. Add the sliced onions, sugar, and remaining 1/2 teaspoon salt. Cook for 30 to 40 minutes, stirring often, until the onions are deeply golden brown and jammy. Don't rush this step; the slow cook is where the flavor comes from.

Add the garlic: Stir in the minced garlic and cook for 1 minute, until fragrant.

Toast the orzo: Add the orzo and stir for about 1 minute to lightly toast it in the buttery onions.

Simmer risotto-style: Pour in the beef broth, Worcestershire, and thyme. Bring to a simmer and cook for 12 to 14 minutes, stirring often, until the orzo is tender and the broth has thickened into a creamy sauce.

Melt in the cheese: Return the chicken and any juices to the skillet. Stir in the gruyere and Swiss until melted and the orzo is coated in that stringy, cheesy sauce.

Broil and serve: For a bubbly, golden top, slide the skillet under the broiler for 2 to 3 minutes, watching closely. Sprinkle with parsley and serve warm from the pan.