In large heavy skillet, melt butter and olive oil over medium high heat. Brown turkey legs and transfer to crock pot. Add onion, celery, garlic and carrots to the skillet and cook until slightly softened, about 5 minutes. Add wine and bring to a boil make sure to scrape up any brown bits. Let wine reduce for 2-3 minutes then add herbs and cook for 30 seconds. Transfer mixture into crock pot, season with salt and pepper. Cover and cook on high 2-3 hours ( or Low for 4-6 hours).

To finish the gravy: Transfer turkey legs and vegetables to plate when done and cover to keep warm. Pour the sauce through a strainer into a small saucepan and bring to a boil for 5 minutes. Mix the cornstarch with 2 Tablespoons of water, then add to the sauce. Bring to a boil and cook until it thickens, about 2 minutes.Remove from heat, stir in cream until it is hot or the butter just until it melts. Serve.