Melt butter in a 12-inch skillet over medium-high heat. Add onion, carrot, celery and garlic and cook until onion is soft, about 8 to 10 minutes.

Stir in flour and cook until golden, about 2 minutes. Stir in 1 cup of broth and scrape up any browned bits and smooth out any lumps; transfer to slow cooker.

Stir in remaining broth, water, wine, sage, and bay leaves into the slow cooker.

Season turkey with salt and pepper, place skin side up in the slow cooker, cover and cook 5 to 7 hours on low, or until the turkey reaches 165°F with an instant-read thermometer.

Transfer turkey to a cutting board tent loosely with foil and let it rest 20 minutes.

Let braising liquid settle for 5 minutes, then remove the fat from the surface using a large spoon or a gravy fat separator.

Strain braising liquid into saucepan, discard celery, bay leaves and simmer until thickened, about 15 minutes. Season with salt and pepper to taste.

Discard the skin and carve the turkey and serve with gravy.