Cook 1 diced shallot in butter, 2 minutes. Add 1/2 diced green apple; cook 1 minute. Add 1 teaspoon chopped parsley, then let cool. Mash 6 hard-boiled egg yolks, the apple mixture, 2 tablespoons mayonnaise, 1/2 teaspoon dijon mustard, and salt and pepper. Spoon into the egg whites; top with lemon thyme or mint.