Mama s Summer Squash Casserole

8 yellow summer squash, thinly sliced

1 small yellow onion, thinly sliced

1 egg, lightly beaten

1 cup low-fat sour cream

1 sleeve buttery round crackers (such as Ritz®), crushed, divided

2 cups shredded sharp Cheddar cheese, divided

Preheat oven to 350 degrees F (175 degrees C). Grease a 1-quart casserole dish.

Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add squash and onion, cover, and steam until squash is tender and easily mashed with a fork, 10 to 15 minutes.

Whisk egg and sour cream together in the prepared casserole dish; add squash, onions, 2/3 the crackers, and 2/3 the Cheddar cheese. Stir with a fork. Cover the squash mixture with remaining Cheddar cheese and crackers.

Bake in the preheated oven until cheese is melted and crackers are lightly browned, about 30 minutes.