Cook first 3 ingredients in boiling water to cover in a Dutch oven 25 minutes or until squash is very tender. Drain well, and mash mixture with a fork.
Crush 10 crackers, and stir into squash mixture; stir in 1/2 cup cheese and next 5 ingredients. Spoon mixture into a lightly greased 11- x-7-inch baking dish.
Crush remaining 6 crackers, and sprinkle over casserole; sprinkle remaining 1 cup cheese evenly over casserole.
Bake, uncovered, at 350° for 30 minutes or until cheese melts and casserole is bubbly.
Note: To make ahead, prepare recipe as directed; do not top with crackers or cheese. Cover and chill overnight. Remove from refrigerator; let stand 30 minutes. Uncover and top with crackers and cheese; bake as directed.
Like most, I made modifications, for various reasons. My variations were some extra onions (using a mistake in another recipe cooking at the same time), multi-grain wheat thins instead of saltines, and using two different cheeses by accident. I used Havarti and Asiago, both of which happened to work out well for their areas of the casserole. I also could have used more crackers and/or drained the squash a bit more to get a thicker consistency, but it's really good as it is. I actually didn't get to taste it fresh, but it is fabulous reheated and goes to the top of my recipe list.
This was a hit with my family and so easy! I even threw in a stray zucchini that I had on hand for some extra color. Be sure to drain the squash very well. I added about 6 extra crackers to get the consistency that I wanted.