01 - Preheat oven to 425°F. Line a large baking tray with parchment paper.
02 - Toss halved baby potatoes with 2 tbsp olive oil, rosemary, thyme, garlic powder, salt, and pepper. Spread in a single layer on the prepared tray and roast for 30–35 minutes, turning halfway through, until crispy and golden.
03 - While the potatoes roast, season the chicken breasts on both sides with salt and freshly ground black pepper.
04 - Heat 2 tbsp olive oil in a large skillet over medium-high heat. Sear the chicken breasts for 4–5 minutes per side until golden and nearly cooked through. Remove from the skillet and set aside.
05 - Reduce heat to medium. Add 1 tbsp butter to the skillet, then sauté the mushrooms and shallot for 4–5 minutes until the mushrooms soften and begin to brown. Add the minced garlic and cook for 1 additional minute.
06 - Pour in the chicken broth to deglaze, gently scraping up any browned bits from the bottom. Simmer until the liquid reduces by half, about 3–4 minutes.
07 - Stir in the heavy cream, Dijon mustard, and thyme. Return the chicken breasts to the skillet and simmer for 6–8 minutes until the sauce thickens slightly and the chicken is cooked through to an internal temperature of 165°F.
08 - Taste the sauce and adjust seasoning with salt and pepper as needed. Garnish with chopped fresh parsley.
09 - Serve the chicken smothered in creamy mushroom sauce alongside the crispy herb-roasted potatoes. Sprinkle the potatoes with additional fresh parsley before serving.