From Darina Allenís Ballymaloe Cooking School Cookbook
While the roast is cooking, make the horseradish sauce.
1-1/2 to 3 tablespoons horseradish root, scrubbed, peeled, and grated
1 tsp wine vinegar
1 tsp lemon juice
1/4 tsp mustard
1/4 tsp salt freshly ground black pepper
1 tsp sugar
1 cup softly whipped cream
Put the grated horseradish into a bowl along with the vinegar, lemon juice, mustard, salt, pepper, and sugar. Fold in softly whipped cream but do not overmix or it will curdle. It keeps for 2 to 3 days, but cover it tightly so it does not pick up other flavors in the refrigerator.