Stuffed Acorn Squash with Sausage

Gather all ingredients. Preheat the oven to 375 degrees F (190 degrees C). Line a baking sheet with aluminum foil.

Place squash halves, cut-side down, onto the prepared baking sheet. Bake in the preheated oven until tender, about 1 hour. Remove from the oven, turn squash halves over, and set aside to cool. Leave the oven on.

Heat a large skillet over medium-high heat. Add sausage; cook and stir until browned and crumbly, 5 to 7 minutes; drain and discard grease. Add celery, mushrooms, and onion; cook and stir until celery is softened, 5 to 10 minutes. Remove from the heat.

Beat egg in a large bowl; stir in sour cream and Parmesan cheese. Stir cheese mixture into sausage mixture, then spoon into squash halves.

Return to the oven and bake until filling is cooked through, about 20 minutes.