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 170F, 4 to 5 hours.
Transfer to a cutting board and tent with foil.
Let rest 15 minutes.
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.