How to Make It
Preheat the oven to 425° and line a roasting pan with parchment paper. Rub the inside of each squash half with 1 tablespoon of the butter and press a sage leaf onto each one. Season the squash with salt and pepper and place cut side down in the roasting pan. Add 1 cup of water to the pan. Cover with foil and roast for 1 hour, until tender. Let cool. Discard the sage and scoop the flesh into a bowl.
In a small skillet, melt the remaining 4 tablespoons of butter. Add the remaining 4 sage leaves and cook over moderate heat until the butter is lightly browned, about 5 minutes. Transfer the sage to a plate.
Add the browned butter and lemon juice to the squash and mash to a puree. Season with salt and pepper. Transfer the squash to a bowl, drizzle with balsamic vinegar and garnish with the fried sage leaves.