In a medium bowl, beat egg yolks, Dijon, vinegar, and 1 teaspoon salt with a mixer at medium-low speed. With mixer running, add oil in a slow, steady stream, and beat until mixture is thickened and well combined, 1 to 2 minutes. Stir in parsley and dill. Transfer mayonnaise to an airtight container and refrigerate until ready to use or for up to 3 days.
Spread about 1 tablespoon mayonnaise on one side of each bread slice. Place 2 tomato slices on each of 5 bread slices. Sprinkle tomato with salt and pepper. Top with remaining bread slices, mayonnaise side down.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/classic-tomato-sandwiches/