1  pound Sweet potatoes or yams (about 3 medium)    (1 can 18 oz yams can be substituted)
1/2  cup sour cream
1/2  teaspoon salt
1/4  teaspoon ground mace
    1  egg yolk
1/4  cup miniature marshmallows

Wash sweet potatoes but do not pare.  Heat enough salted water to cover sweet potatoes to boiling.  Add potatoes.  Cover and heat to boiling; reduce heat.  Boil until tender, 30 to 35 minutes; drain.  Slip off skins.  Beat sweet potatoes, sour cream, salt, mace and egg yolk on medium speed until smooth.  Pour into buttered 1 quart casserole; top with marshmallows.  Bake uncovered in 350F oven until marshmallows are puffed and golden brown, about 30 minutes.
Yield: 5 servings.