Preheat oven to 400°F. Pat chicken thighs dry and trim any excess fat.
In a small bowl, combine the onion powder, garlic powder, thyme, rosemary, salt and pepper. Rub the seasoning blend all over both sides of the chicken thighs.
Heat 1 Tbsp olive oil in a large oven-safe skillet or dutch oven over medium-high heat. Add chicken thighs in a single layer and sear for 2-3 minutes per side until browned. Work in batches if needed, adding more oil for the next batch.
Transfer seared chicken to a plate. In the same skillet, melt the butter over medium heat. Add mushrooms and season with salt and pepper. Sauté for 3 minutes until starting to brown.
Add garlic, thyme and rosemary. Cook for 1 minute until fragrant. Pour in cream and Parmesan. Bring to a simmer, stirring frequently, until sauce thickens slightly, about 2-3 minutes.
Return chicken and any accumulated juices to the skillet, coating chicken in the mushroom sauce. Transfer to the oven and bake for 15 minutes until chicken is cooked through.
Remove from oven and garnish with fresh chopped parsley. Serve chicken with plenty of the luscious mushroom sauce spooned over the top or on the side.