Preheat the oven to 350°F. Lightly grease a casserole dish with 1 tablespoon of butter.
In a large bowl, whisk together the half-and-half, cream, eggs, and orange zest.
Add the granulated sugar, 4 tablespoons of brown sugar, salt, ginger, cinnamon, nutmeg, vanilla, and Grand Marnier. Whisk vigorously until fully combined.
Add the pumpkin and whisk until smooth.
Fold in the bread and let it soak for 10 minutes, stirring occasionally to coat evenly with a spatula.
Pour the mixture into the prepared casserole dish.
Melt the remaining 2 tablespoons of butter and drizzle over the top.
Sprinkle with the remaining 2 tablespoons of brown sugar.
Bake for 40 minutes, or until the pudding is set and golden brown.
In a small bowl or deli container, whisk together the bourbon and cornstarch. Set aside.
In a saucepan, combine the half-and-half, heavy cream, sugar, and vanilla.
Heat over medium-high, whisking constantly, until bubbles form around the edges.
Remove from heat and whisk in the bourbon-cornstarch mixture until smooth.
Return the pan to low heat and cook, whisking continuously, until the sauce thickens slightly, about 3 minutes.
Remove from heat and continue whisking for a minute or two as it cools slightly.
Serve warm over the bread pudding and enjoy!