Over medium heat, add the olive oil and butter to a heavy-bottom, oven-safe skillet and melt the butter into the oil.
Lightly salt and pepper both sides of the chicken thighs. Carefully lay the thighs, skin side down, in the skillet and sear for 3-4 minutes. Turn once, sear for another 3-4 minutes and remove from the skillet. Set aside.
Add the onions and mushrooms to the skillet. Sauté until the mushrooms are browned.
Add the garlic and cook for one minute.
Add the canned mushroom soup, heavy cream, two tablespoons of water, and dried thyme. Stir into the mushroom and onion mixture.
Nestle the chicken thighs into the mushroom sauce and bake for 40 minutes.