Ever-so-slightly undercook the squash. It should have a slight crunch, and not be mushy. The squash will continue to soften while the casserole is baking. The casserole can be assembled ahead of time and stored in the fridge. Before serving, place in the oven. You will need to increase the baking time by likely 15-20 minutes.
You won't believe there isn't actual cream in this divinely comforting casserole. Feel free to add your choice of cooked protein (ground sausage is delicious!) to make a complete meal out of this casserole.