Zucchini Casserole

This recipe will feed an army of hungry people! This will feed 12+ people, easy to reduce the ingredients or you can have a lot of leftovers ;)

1 1/2 TBSP margarine or butter, unsalted
1-2 large red onion, chopped
1 1/2  C celery, chopped
3 LBS medium zucchini, halved lengthwise and sliced
1  TSP salt
1  TSP ground thyme
1/4 TSP hot red pepper flakes
3/4 TSP pepper
3 TBSP cornstarch   
3/4 C fat free half and half
3/4 C reduced fat sour cream
1/2 C sharp cheddar cheese, shredded, divided
3/4 C bread crumbs

Preheat oven to 350 degrees F.
In a large skillet over medium heat, melt the margarine. Add the onion and celery and cook, stirring often, until tender, about 5 minutes. Add the zucchini, salt, thyme, red pepper flakes, and pepper. Cook until the zucchini is just tender, 8 to 10 minutes.
In a cup, dissolve the cornstarch in the half and half. Pour over the zucchini and cook, stirring, until thickened and coating the vegetables, about 2 minutes.
Remove from the heat and stir in the sour cream and about 3 tablespoons of the cheese. Scrape into large baking dish. Mix together the bread crumbs and remaining cheese. Sprinkle evenly over the top.
Bake until bubbly, about 20 minutes. Turn on the broiler and broil until the top is lightly browned, about 1 minute