Shepherds Pie is usually made with minced lamb or beef meat and savoury vegetables.
Go for a wine with good acidity to cut through the fat and enough fruit to elevate the meat taste.
The Sour Cherry flavors of Chainti will help to smooth the gamey taste of the lamb.
North Rhone blends have some peppery Syrah. They are a great match to lamb.
Bordeaux and Lamb are a classic match. Try a lighter, Claret style, Bordeaux to accompany this dish. The bolder, jammy style with high alcohol might be too dominant.