1 1/2 cups mayonnaise, divided
2 tablespoons mustard
1/2 cup chopped scallions, divided
2 tablespoons flour
1 cup milk
12 eggs, separated
1/2 teaspoon salt
1/8 teaspoon pepper
Cooking spray
1 1/2 cups finely chopped ham
1 cup shredded Swiss cheese
Watercress to garnish (optional)

Combine 1 cup mayonnaise, mustard and 1/4 cup scallions. Mix well and set aside.

Combine remaining mayonnaise and flour. Gradually add milk and beaten egg yolks. Cook, stirring constantly over low heat, until thickened. Remove from heat and cool 15 minutes. Beat egg whites until stiff. Fold mayonnaise mixture, salt and pepper into whites, combining thoroughly. Pour into a 15 x 10-inch jellyroll pan lined with wax paper coated with cooking spray. Bake at 425 degrees F for 20 minutes.

Invert on towel; carefully remove the wax paper. Mix the ham, cheese and 1/4 cup scallions together and spread on the roll. Roll from narrow end, lifting with towel while rolling. Place on serving dish seam down and top with the mustard sauce. Garnish with the greenery of your choice. Watercress is especially nice.

Yields 6 to 8 servings.