Squash Casserole

This started out as a stuffed onion recipe I found years ago, we tried it for Thanksgiving that year & decided we liked the "filling" but stuffing it into onions was more trouble than it was worth, so we turned it into a squash casserole instead. Here's our final version:

6 c 3/4" chunks peeled pumpkin or butternut squash
chopped onion (original recipe used the "flesh" from 6 of the onions for stuffing, so maybe 3 good sized onions?)
3 T butter
1/4 tsp salt
3 T finely chopped fresh sage leaves (about 12 lg) or 2 tsp dried
6 oz (1 1/2 c) shredded cheese (swiss, mozarella or a mix, or really whatever you have, the original recipe called for Gruyere but I'm too cheap to buy it for something where the flavors all blend together anyway.
Garnish: fresh sage leaves
Put squash cubes in med saucepan; add water to cover. Bring to a boil, reduce heat, cover & simmer 15-20 min. till tender. Drain well, then mash. Meanwhile, melt butter in lg skillet over med heat. Add chopped onions, salt. Sauté 9-10 min. stirring often, till browned & tender. Stir in sage. Stir onion mixture, 1/4 c cheese into squash. Spoon mixture into casserole. Bake uncovered 20 min. at 375. Top w/ remaining 1/4 c cheese & bake 5 min. or till cheese melts. Garnish w/
sage leaves.