1. Heat oven to 450 degrees with the rack in center. Halve squash lengthwise, and remove seeds and fibers. Sprinkle squash halves with 1/2 teaspoon salt and 1/4 teaspoon pepper. Fill a roasting pan with 1/4 inch water. Place squash in pan. Cover with aluminum foil, and bake until squash is tender when pierced with the tip of a knife, 35 to 45 minutes. Remove from oven, transfer squash to a cool surface, and let cool enough to handle. Reduce oven temperature to 425 degrees.

2. Use a spoon to scoop baked flesh out of each half into a large bowl, leaving a 1/4-inch border around six of the halves so they will keep their shape. To the bowl, add sour cream, paprika, chives, and remaining teaspoon salt and 1/4 teaspoon pepper. Mix with a handheld electric mixer or potato masher until smooth and well combined. Season with salt and pepper. Fill six squash halves with mixture (discard remaining six empty halves). Sprinkle tops with toasted breadcrumbs. Bake until golden brown and warm throughout, 20 to 30 minutes. Serve.