The amounts here will depend on how much squash you are using, and how large it or they are. It’s a puree–it’s forgiving.
fresh sage leaves, chopped, if you have them
1/2 to 3/4 c milk, as needed
4 T butter, or more, to taste
salt and pepper, to taste
1. Preheat the oven to 400ºF. Cut the squash in half lengthwise. Scoop out the seeds, season the interior with salt and pepper, and fill the cavities with some peeled garlic and chopped sage. Place the squash, cut side up, in a shallow ovenproof dish and add just enough water to barely cover the bottom, to prevent burning. Bake for about 45 minutes, or until completely tender. Remove and discard the sage, but hold onto the garlic. Let the squash cool a bit.
2. Scoop the squash flesh out and mash or puree–by hand or in a food processor (add the garlic if using). In a small saucepan, melt the butter in the milk over low heat. Whisk the buttery milk into the squash puree. Season with salt and pepper.