Preheat the oven to 400 degrees F (200 degrees C). Place butternut squash on a baking sheet, flesh-side up.
Roast in the preheated oven until tender and slightly brown, 45 minutes to 1 hour. Cool until easily handled.
Scoop flesh into a food processor; pulse until smooth. Add stock, 1/4 cup at a time, while continuing to pulse, until smooth or desired consistency. Season puree with salt and pepper.