How to Make the Ultimate Umami-Bomb Vegetarian Demi-Glace
1 cup chopped celery (not too fine)
1/4 pound boiled ham, chopped (not too fine)
3 tablespoons mayonnaise
2 teaspoons mustard or more to taste
6 slices firm-textured white bread, crusts removed
In a bowl, combine the celery, ham, mayonnaise and mustard. Mound the mixture in the center of 3 slices of bread and top with the other slices. Using a large sharp knife, slice the sandwiches on the diagonal.