In a small bowl, combine butter, mustard, and relish, stirring well.
Spread butter mixture onto 1 side of each bread slice.
Place 4 slices corned beef in a ruffled pattern on buttered side of 2 bread slices. Top each with a buttered bread slice, buttered side down. Spread each bread slice with more butter mixture. Top each with another 4 slices corned beef in a ruffled pattern. Top each with a remaining bread slice, buttered side down.†
Using a sharp, serrated knife, cut crusts from sandwich. Cut each sandwich in half and then each half into 4 square pieces.
Garnish each sandwich with a cornichon slice, and secure with a green-frilled toothpick, if desired.
Notes
*For testing purposes, we used Pepperidge Farm Farmhouse Style Oatmeal Bread. †Sandwiches may be made early in the day, left whole, draped with a slightly dampened paper towel, and kept in a covered container in the refrigerator. Slice into individual sandwiches just before serving.
Recipe by TeaTime Magazine at https://teatimemagazine.com/corned-beef-tea-sandwiches-with-mustard-butter-recipe/