When unexpected guests arrive, this is a great casserole to whip up quickly with ingredients you are likely to have on hand in the pantry.
Preheat the oven to 350 degrees F.
Drain the salmon, pouring the liquid into a glass measuring cup. Flake the salmon and place in a large mixing bowl. Add enough milk to the measuring cup to make 1 cup of liquid. Add to the salmon.
Melt 2 tablespoons of the butter in a small skillet over medium heat. Add the onion and green pepper and saute until limp, about 4 minutes. Add to the salmon, along with the eggs, cheese, corn, salt, and pepper. Mix well. Spoon into a 9-inch by 13-inch baking dish.
Melt the remaining 1 tablespoon butter and combine with the crushed crackers. Sprinkle over the top of the casserole. Bake for 45 minutes, uncovered. Serve hot.