Cook the spinach in a small amount of water just until tender. Drain and purée. Cream butter and add to the egg yolks, stirring well. Mix the puréed spinach with egg-yolk mixture and parsley.
Soak bread slices in milk and, using a sieve, press dry. Break up into small pieces and stir into spinach mixture. Add sour cream, salt and pepper to taste, and fold in the egg whites. As you fold, sift in the bread crumbs, reserving 2 tablespoons to coat a buttered mold.
Prepare 2-quart mold and pour in spinach mixture. Cover mold and set in a pan of water which comes halfway up the side of the mold. Steam for about 1¼ hours.
Turn out on a platter and serve hot with melted butter to which plenty of lemon juice has been added.
Serving Ideas : Danes often garnish the platter w/ small boiled artichokes