Salmon-Spinach Pie

1 onion, chopped
2 ribs celery, chopped
butter
1 clove garlic, chopped
1 can cream of mushroom soup
mushrooms, canned (if fresh, sauté with onion and celery)
1 pkg. (8 oz,) spinach, frozen (thawed) or fresh (if fresh sauté with onion and celery)
3 medium potatoes with skin on, cooked and cubed
1 can salmon
cracked pepper, to taste
2 boxes jiffy corn muffin mix, mix according to directions with eggs and milk

Sauté onion and celery with mushrooms and spinach in butter in a cast iron or other oven-proof skillet.  Add garlic at end of cooking time.  Stir in canned soup and mushrooms and spinach, if not using fresh.  Fold in potatoes and salmon.  Pour jiffy mix over all and bake in oven at 400 for 15-20? minutes or until cornbread topping is golden.