Preheat the oven to 325ºF.
Cut the squash in half lengthwise and scoop out the seeds. Place the squash, cut side down, on a rimmed baking sheet with just enough water to cover the bottom. Transfer the squash carefully to the oven and bake for 25 minutes. Remove it from the oven equally carefully; the water should have evaporated, but you could splash yourself if any remains. Remove the squash from the sheet and allow it to cool at room temperature, cut sides up, until ready to use.
Just before serving, set the squash, cut side down, on the grill directly over the coals of a small wood-infused fire. Grill for 3 to 4 minutes, then flip, moving the squash to the coolest part of the grill. Add 1 Tbs. butter to each half, season to taste with salt, and drizzle on the molasses. Cover the grill and cook until the butter is melted, about another 2 minutes.
Take the squash off the grill and, using tongs, squeeze the squash halves to release the flesh. Use a fork to gently shred it and mix it with the butter. Serve immediately in the shells.