STIR brown sugar and salt in a bowl. Rinse turkey and dry very well with paper towels. Place turkey in a large pan or large plastic bag, then pack brown sugar mixture all over the outside of the turkey as best you can, and place some in the cavity as well. Cover pan or tie bag, and refrigerate 12 hours or overnight.
PREHEAT oven to 450F. Rinse brine from the turkey, inside and out, gently rubbing under cold running water so it all comes off. (Don’t worry if the legs and wings look purple, which is the result of brining.) Pat dry. Stuff sage into cavity.
PLACE turkey on a rack in a roasting pan. Bend and tuck wings under the body and loosely tie drumsticks together. Brush butter all over turkey. Loosely cover with foil. Roast for 30 min. Reduce oven temperature to 325F. Roast until an instant-read thermometer inserted into the thickest part of the thigh reads 175F, about 2 1/2 to 3 1/4 hours. Remove foil during final hour of cooking.
TRANSFER turkey to a platter, tent loosely with foil and let rest at least 25 min before carving.
FOR GRAVY: carefully spoon most of the fat out of the roasting pan, leaving behind about 4 tbsp fat as well as all the brown bits. Place the pan on the stove over medium and stir in flour, whisking to completely incorporate flour into drippings. Cook for 30 sec, then whisk in wine and water. Increase heat to medium-high, whisking constantly, until thickened, scraping up and incorporating all the brown bits from the pan, about 10 to 15 min. Reduce heat to low. If needed, whisk in additional water or homemade turkey stock to reach the desired consistency. Season to taste with salt and pepper.
Kitchen tip: Brining is a chef’s trick for improving flavour and texture, and this dry method is easier than the wet method. It’s essential to use kosher salt and to rinse all traces of the sugar-salt mixture from the bird before roasting. Another way to get a perfect roast turkey is to buy a fresh bird. Naturally raised or organic turkeys can be even more juicy and flavourful.