Tuna Melts with Horseradish Mayonnaise
- 6 tablespoons mayonnaise
- 2 6 -ounce cans solid white tuna, drained
- 1/4 cup finely chopped celery
- 2 scallions, finely chopped
- 2 tablespoons finely chopped fresh parsley
- 2 teaspoons apple cider vinegar
- Kosher salt and freshly ground pepper
- 1 tablespoon whole-grain mustard
- 1 tablespoon prepared horseradish
- 4 large slices rye bread, lightly toasted
- 8 thin slices havarti cheese
- 2 tomatoes, cut into 8 slices
- Dill pickles, for serving (optional)
Position a rack in the upper third of the oven and preheat to 475 degrees F. Combine 4 tablespoons mayonnaise, the tuna, celery, scallions, parsley and vinegar in a large bowl and mix well. Season with salt and pepper.
Combine the remaining 2 tablespoons mayonnaise with the mustard and horseradish in a small bowl; spread on the bread slices and arrange on a baking sheet. Mound the tuna mixture on top and pat it into an even layer. Top each with 1 cheese slice, tearing it as needed to cover the tuna mixture.
Season the tomato slices with salt; place 2 slices on top of each sandwich, then top each with another cheese slice. Bake until the cheese melts, 5 to 7 minutes. Serve with dill pickles.