1. Stir broth, wine, lemon juice, garlic and thyme in slow cooker. Add vegetables. Rinse turkey in cold water; pat dry. Brush turkey with some of the butter; sprinkle with salt. Place turkey in cooker, meaty side up; drizzle with any remaining butter. Cover and cook on low until a thermometer inserted into center of breast reads 170ºF, 4 to 5 hours. Transfer to a cutting board and tent with foil. Let rest 15 minutes.
2. Strain cooking liquid into a pan. Remove 1/4 cup of liquid; whisk with cornstarch until smooth. Stir cornstarch mixture into pan. Bring to a boil, whisking; cook until thickened, 2 to 3 minutes. Season with salt. Slice turkey; serve with gravy.