Shepherd’s Pie with Northern Isles Lamb Sausage and Potato-Horseradish Crust

Shepherd’s pie is a signature dish in the pubs of England and Ireland, sometimes made with lamb, as here, and sometimes with beef, in which case it is called cottage pie. The idea is the same: a simple meat pie made with a mirepoix—onion, carrot, celery—under a top crust of mashed potatoes. There’s no cheese in the mashed potatoes, but when the pie is baked, the crust is somehow enriched through the alchemy of cooking and tastes as though there were. Shepherd’s pie is usually made with leftover cooked lamb. Swapping that for quick and easy homemade lamb sausage is my revisionism, to give the humble pie a fresh and lively taste. Also, to gussy it up, I use tiny pearl onions so the onion element has a more defined presence in the pie. The horseradish is also my whim, to give the dish an acrid lilt that helps lift it above what might otherwise be humdrum fare. Fresh horseradish root is often available in produce stores and supermarkets around Passover for Jewish customers; wasabi root, though not exactly the same botanically, is similar and it is available around the New Year for Japanese customers. Like fresh ginger, horseradish root can be stored in the refrigerator almost indefinitely, as long as it is kept dry.