Tuna Melt

I noticed we needed more sandwich recipes so here's my old favorite, the Tuna Melt. You can use whatever type bread you like but I think the sliced sourdough holds up better to the moist filling.

1 can albacore tuna in water, drained well
1/2 small onion minced
1/4 cup finely chopped celery
1 mediun dill_pickle finely diced
1/4 cup mayonnaise
2 tsp brown mustard
1/8 tsp black pepper
4 slices cheddar_cheese
Softened butter
8 slices sourdough bread (pre sliced such as Toscana)