Preheat the oven to 400°F (200°C). Toss baby potatoes with olive oil, rosemary, salt, and pepper; spread on a baking sheet and roast for 25-30 minutes until golden and tender.
Season chicken breasts with salt and pepper. In a large skillet, melt butter over medium heat and cook chicken until golden on both sides and cooked through, about 6-7 minutes per side. Remove and set aside.
In the same skillet, add garlic and sliced mushrooms. Cook until mushrooms release moisture and become tender, about 5 minutes.
Pour in heavy cream and add fresh thyme. Simmer the sauce for 5 minutes until it thickens slightly.
Return the chicken breasts to the skillet and coat them in the creamy mushroom sauce. Cook together for 2-3 minutes to heat through.
Serve the creamy mushroom chicken alongside the herb roasted potatoes. Garnish with extra thyme if desired.
Notes
For extra flavor, marinate the chicken for 30 minutes in olive oil, garlic, and herbs before cooking. Leftover sauce makes a great topping for steamed vegetables.