Mustard-Rubbed Roast Turkey with Mushroom Gravy

Coarsely puree first 7 ingredients in processor. Reserve 1/2 cup mustard mixture in bowl; cover and chill. Rinse turkey inside and out; pat dry. Slide hand under skin of turkey breast, legs and thighs to loosen skin. Using hand, spread 1 cup mustard mixture under skin over turkey breast, legs and thighs. Spread remaining mustard mixture inside main cavity. Place turkey on rack in large roasting pan. Slide pan with turkey into large plastic bag (about 30-gallon capacity). Close bag; refrigerate turkey at least 1 day and up to 2 days. Position rack in bottom third of oven; preheat to 325 °F. Remove pan with turkey from bag. If stuffing turkey, spoon stuffing loosely into main cavity. Tuck wing tips under turkey; tie legs together loosely. Spread 1/2 cup chilled mustard mixture all over turkey. Roast 2 hours. Baste with 1/2 cup broth. Continue to roast until turkey is brown and thermometer inserted into thickest part of thigh registers 180 °F, basting frequently with remaining 1 1/2 cups broth and pan juices and covering loosely with foil if browning too quickly, about 1 hour 30 minutes longer if unstuffed and 2 hours longer if stuffed. Transfer turkey to platter. Tent loosely with foil; let stand 30 minutes. Reserve pan juices for gravy.