For centuries, going back to Anglo-Saxon times, holiday revelers have wished each other “Wes hal!” — Be Whole! — while sharing this drink. Wassail traditionally contained roasted apples, which would swell up and burst apart in the hot punch, giving it the name Lamb’s Wool.
Preheat oven to 400° F. Cut the apples into thick slices, and arrange in layers in a covered casserole dish, sprinkling a few teaspoons of sugar over each layer. Cover and bake for 30 minutes. (The apples will get puffy and soft.)
While the apples bake, combine the beer, spices, lemon zest, and remaining sugar in a large saucepan. Heat slowly, bringing just to a simmer. (Don’t let the mixture boil.) When it is hot, add the sherry and keep heating until the mixture reaches a simmer again, still not boiling. Place the hot baked apples in a punch bowl, and pour the hot wassail over them. Serve hot.