Olive oil
Salt and pepper, to taste
2 tbsp. fresh chopped parsley
2 tbsp. fresh chopped sage, plus whole leaves for topping later
2 ribs celery, diced
1 onion, diced
1 stick unsalted butter
6 oz. sourdough bread, cubed small
2 1/3 cups milk, divided
1 egg
8.5 oz. corn muffin mix, especially Jiffy