Roasted Turkey Breast

Preheat oven to 400. Rinse turkey breast with cold water; pat dry with paper towels; rub butter on skin side of turkey breast. Place in a shallow ovenproof dish, skin side down. Combine mustard, sour cream, salt and pepper; rub on the non-skin side of turkey breast. Cover with foil; place in the refrigerator for one hour to marinate. Roast skin side down for 20 minutes per pound. The turkey is done when an instant-read thermometer inserted in thickest part of breast reads 160. Remove from oven; let stand at least 20 minutes before carving.