Soft, white breadcrumbs are the secret to this classic casserole's tender, soufflé-like texture. To make fresh breadcrumbs, tear day-old slices of sandwich bread into pieces, and pulse several times in the food processor until coarse crumbs form.
2 pounds yellow squash, sliced
2 pounds zucchini, sliced
1 large sweet onion, finely chopped
2 cups (8 oz.) shredded sharp Cheddar cheese
2 cups soft, fresh breadcrumbs
1 (8-oz.) container sour cream
2 large eggs, lightly beaten
1 1/2 teaspoons garlic salt
1/2 teaspoon freshly ground pepper
3/4 cup (3 oz.) freshly shredded Parmesan cheese
How to Make It
Cook first 3 ingredients in boiling water to cover in a Dutch oven 10 to 12 minutes or just until tender; drain well in a colander, gently pressing squash mixture against sides with a wooden spoon.
Stir together squash mixture, Cheddar cheese, and next 5 ingredients. Spoon into a lightly greased 6-qt. oval-shaped slow cooker. Sprinkle Parmesan cheese over top.
Cover and cook on LOW 2 1/2 to 3 hours or until center is set and edges are golden brown; uncover and cook 30 minutes. Let stand 10 minutes.
Note: Yellow squash, zucchini, and onions may be cooked and drained as directed up to 2 days ahead. Cover and chill until ready to assemble casserole.