Mashed Squash and Potatoes with Amaretti

INGREDIENTS

2 lb

russet potatoes, peeled and cut into 1-inch cubes (about 6 cups)

Coarse salt

3 lb

buttercup squash (about 1 small squash), peeled, seeded, and cut into 1-inch cubes (about 8 cups)

6 tbsp

unsalted butter, plus more for baking dish

1/2 cup

heavy cream

1/4 tsp

freshly ground nutmeg

Freshly ground pepper

1/2 cup

finely grated Parmigiano-Reggiano cheese

Amaretti (Italian almond cookies), crushed into fine crumbs (about 3/4 cup)