Preheat oven to 350 F. Butter six 10-ounce ramekins or custard cups, sprinkle each with 1 tablespoon brown sugar, and set them aside on a baking sheet.
Place raisins in a small bowl, and cover with bourbon, (if using bourbon) and the hot water; let soak until plump, about 20 minutes. Drain; set aside.
In a large bowl, whisk together pumpkin, eggs, granulated sugar, milk, vanilla, spices and salt. Toss in the bread cubes, and stir gently to evenly coat; let stand a few minutes. Fold in the raisins. Divide mixture among ramekins or custard cups, pressing down slightly to make level.
Bake until custard is set in the center and top is golden, about 40 minutes. If bread browns too quickly, cover loosely with aluminum foil. Remove from oven; let cool slightly.
To serve, un-mold onto plates; dust with confectioners’ sugar.