Bisect the butternut squash "long ways." Scoop out and discard seeds. Drizzle with 1 tablespoon of the extra virgin olive oil. Season liberally with salt and pepper.
Take the half-head of garlic, and slice off the top ¼ of the head exposing the cloves inside. (No need to peel each one.) Place head into foil pouch, and drizzle with the remaining 2 tablespoons of extra virgin olive oil. Seal up pouch.
Roast both garlic and squash (face down) in the oven at 400° for 30 minutes. The butternut squash may need to roast an additional 10 minutes longer based on its size. The squash should be fork-tender when done. Remove both from the oven, and allow to cool.
Bring the dough up to near room temperature. I usually purchase in the bakery area of Wegmans or Giant. Steer clear of the frozen dough. Buy fresh right from the baker. Hold the dough, pressing around your fist, stretching it out to a round area of about 12".
Once cooled, scoop out the butternut squash soft center and mash in a bowl; adding salt and pepper to taste. Do the same with garlic, removing each clove from its casing and mash in a separate both with the half-stick of butter.
Spread the garlic butter as the base of the flatbread, leaving ¼" spacing on the outside as a crust. Top with the butternut squash paste, then top with freshly shredded mozzarella cheese. Don't be afraid to take the cheese right to the edge of the crust.
Bake on pizza stone (or pan) in the oven at 400° for 20 minutes or until cheese begins to brown.
Cool for 5 minutes before cutting to prevent cheese from running. Sprinkle with fresh sage.