Preheat the oven to 350?F. Lightly grease an 8-cup ovenproof casserole or mold with 2 teaspoons of the butter.
In a large bowl whisk together the half-and-half, cream, eggs, and orange zest. Add all of the granulated sugar, 4 tablespoons of the brown sugar, the ginger, cinnamon, nutmeg, vanilla, and Grand Marnier, and whisk vigorously until thoroughly blended. Add the pumpkin and whisk until incorporated. Fold in the bread and walnuts and mix thoroughly.
Pour the mixture into the casserole, dot the top with the remaining 1 tablespoon butter, and sprinkle with the remaining 2 tablespoons brown sugar. Place the casserole in a water bath (a larger baking dish with about an inch of hot water). Bake until golden brown and puffy, for about 1 hour 15 minutes.
About 15 minutes before the pudding is finished baking, prepare the Kentucky Bourbon Sauce.
Serve warm or at room temperature. To serve, spoon the pudding into bowls or wineglasses, add 2 tablespoons of the Kentucky Bourbon Sauce, and top with a mint sprig.
Yield: 8 generous servings