In a small bowl, mash the remaining egg yolk. Add the sour cream, pickle relish, mayonnaise, mustard, and salt (if desired). Stir to mix well. Stir in the celery.
Chop the egg whites and stir them into the yolk mixture.
Spread the mixture on each slice of bread. Serve as open-faced sandwiches. If desired, garnish with a light sprinkling of paprika.
Notes
If you love egg salad but have cut it from your meal plan because of the cholesterol, try this zippy recipe, and discard half of the egg yolks. With all of the taste of traditional egg salad and far less fat, it's one of this cookbook author's favourite sandwiches.