Spread the cavity of each squash half with about 1/2 teaspoon of the butter, sprinkle the halves with salt and pepper to taste, and arrange them, cut sides down, in a large baking pan. Add enough water to reach about 1/4 inch up the sides of the squash halves and bake the squash in the middle of a preheated 400°F. oven for 30 minutes. While the squash is baking, in a small saucepan combine the remaining butter, the maple syrup, the allspice, the currants, and a pinch of salt and heat the mixture over moderately low heat, stirring, until the butter is melted and the currants are plumped. Remove the squash from the oven, turn it cut sides up, and brush it generously with some of the maple mixture. Return the squash to the oven and bake it, brushing it with the maple mixture occasionally and adding more water to the pan as necessary to keep the bottom covered, for 20 to 30 minutes more, or until it is very tender. Season the squash with salt and pepper.