Cook the chicken: Heat olive oil or butter in a large skillet over medium heat. Season the chicken breasts with salt and pepper. Sear the chicken on both sides for 5-7 minutes per side until golden brown and cooked through. Remove the chicken and set aside.

Cook the broccoli: Steam or blanch the broccoli florets in boiling water for 3-4 minutes until just tender. Drain and set aside.

Make the creamy sauce: In the same skillet, add the minced garlic and sauté for 1-2 minutes until fragrant. Stir in the chicken broth, heavy cream, and Dijon mustard (if using). Bring the sauce to a simmer, allowing it to thicken slightly.

Add cheese and combine: Stir in the Parmesan cheese and fresh thyme or parsley. Continue simmering for 2-3 minutes until the sauce thickens further. Season with salt and pepper to taste.

Combine chicken and broccoli: Return the cooked chicken and broccoli to the skillet, spooning the creamy sauce over them. If desired, sprinkle shredded cheddar cheese on top and cover to allow the cheese to melt.

Serve: Garnish with fresh parsley or chives and serve hot. This dish pairs beautifully with cauliflower mash or zucchini noodles for a complete keto meal.