Preheat oven to 375 degrees
In a large cast iron skillet (10"+) heat 1 Tbs olive oil, until hot but not smoking.
Pat chicken thighs dry, and season with salt and pepper.
Lay chicken thighs into pan, skin down, and cook for 3-5 minutes until skin is golden brown. You want it to be crisp otherwise, the end result will be greasier.
Flip and repeat on other side.
Remove chicken from pan and set aside.
In same pan add another Tbs olive oil and the mushrooms. Make sure mushrooms are cleaned, dry, and sliced.
Saute until browned and slightly tender. Do not over stir.
Add chicken stock and rosemary, simmer for 5 minutes
Bring to a boil, stir well, then turn down to let simmer 10 minutes to thicken up. Add cream to pan. Stir well.
Add Chicken back into the pan.
Put the whole pan into the oven and bake until internal temperature reads 165 degrees, approximately 25-35 minutes
Turn to broil and broil to brown the top and crisp the chicken back up a bit (3-5 minutes)
Remove from oven, and serve immediately.