Cut squash in half lengthwise and remove seeds; place, cut side down, on rimmed baking sheet. Bake in 425F (220C) oven until very tender, 30 to 60 minutes, depending on variety and age of squash. Let cool.

Meanwhile, in large pot of boiling salted water, cook pasta until al dente, about 12 minutes. Drain, rinse under cold water and drain well.

Peel squash; place flesh in bowl and mash well. Mix in cream, salt, nutmeg and pepper. Fill one shell with heaping 2 tbsp (30 mL) of the squash mixture; repeat with remaining squash mixture (about 24 pieces). Place, seam side up, in buttered 12-cup (3 L) casserole dish.

In small saucepan, melt butter and pinch salt over medium heat; cook until butter is light nutty brown; add sage and cook, stirring, for 10 seconds. Pour immediately over shells; cover with foil. (Make-ahead: Let stand at room temperature for up to 4 hours or refrigerate up to 1 day; bring to room temperature before baking.) Bake in 450F (230C) oven until piping hot, 20 to 25 minutes.

Makes 8 to 12 side servings.