Preheat the oven to 350°F.
Heat olive oil in a large oven-safe skillet over medium heat.
Season chicken thighs with sea salt and black pepper on both sides.
Place chicken skin side down in the skillet and cook until skin is browned, then flip and cook for 2 more minutes.
Remove chicken from skillet and set aside on a plate.
Add diced onion to the skillet and cook until softened.
Stir in chicken broth, lemon juice, garlic, thyme, and rosemary.
Return chicken to the skillet skin side up.
Transfer skillet to the oven and bake for 40 to 45 minutes, until chicken is tender and falls apart.
Remove chicken to a plate and set aside.
Whisk cornstarch into the skillet sauce over medium heat and cook until thickened.
Serve the chicken with the thickened sauce and enjoy.