Preheat the oven to 325'
Place squash in large sauce pan.
Add a dash of salt and pepper.
Add water to cover squash.
Bring water to a boil and boil for 1-2 minutes.
Reduce temperature to medium-high heat and cook squash for 20 minutes (or until tender)
Drain well.
Return to stove and mash squash with a fork or potato masher and drain again.
Add diced sweet onions, butter, celery salt, shredded cheese and evaporated milk.
Stir well
Pour squash mixture into a greased 8x8 casserole dish.
Sprinkle the top of the squash mixture with Ritz cracker crumbs.
Cook for 25-30 minutes.
You can definitely use pre-packaged, shredded cheese, however, I find the flavor and texture of this dish is better when you grate the cheese yourself before cooking.