Corned Beef with whites

12 ounces leftover cooked corned beef , cut into 1/2 inch cubes 1 lb baking potato , peeled, cut into 1/2 inch cubes 1/2 teaspoon salt 1 tablespoon butter 1[...]

1/2 cup finely chopped celery 1/2 cup finely chopped green bell pepper 1/2 cup finely chopped onion 2 tablespoons butter or 2 tablespoons margarine 8 slices[...]