Preheat the oven to 350°F
Grease a baking dish
Slice squash and onion
Boil or steam squash until tender
Drain the squash well
Sauté onion in butter until soft
Mash the squash lightly
Mix squash, onion, eggs, shredded cheese, sour cream, salt, and pepper
Stir in crushed crackers or breadcrumbs
Transfer the mixture to the baking dish
Top with more crackers, breadcrumbs, or cheese if desired
Bake for 25 to 35 minutes
Bake until the casserole is set and the top is golden brown
Let it rest for a few minutes before serving