Prep & Season: Slice the chicken breasts in half horizontally to create 4 thinner fillets. Season both sides generously with garlic powder, onion powder, salt, and pepper.
Sear: Heat olive oil and 1 tbsp of butter in a large cast-iron skillet over medium heat. Cook the fillets for 5 minutes per side (or until the internal temperature reaches 165°F). Transfer the chicken to a plate.
Aromatics: In the same skillet, melt the remaining 1 tbsp of butter. Add the sliced onions and sauté for 5 minutes until softened and slightly caramelized.
The Sauce: Pour in the chicken broth and add the Boursin cheese. Stir and whisk until the cheese is completely melted and the sauce is smooth. Simmer for 3–4 minutes to let the sauce thicken slightly.
Finish: Return the chicken fillets to the skillet. Spoon the creamy herb sauce over the meat and simmer for another 3–4 minutes to marry the flavors. Serve immediately.