Leave the buns out of the package for 1 to 2 hours, to dry out a bit.
Preheat the oven to 350 degrees F. Butter a 12-inch Dutch oven or 9.13-inch casserole dish.
Tear the bread into bite-sized pieces and place in a large bowl. Pour the beer over the bread and toss to coat. Cover the bowl and let sit for about 45 minutes to 1 hour to let the beer soak in the bread.
Meanwhile, melt the butter in a medium saucepan over medium heat. Whisk in the cream, vanilla, brown sugar, cinnamon and nutmeg. Cook just until the mixture has warmed, stirring frequently.
Remove from the heat and whisk in the eggs.
Pour the cream mixture into the bread and stir to incorporate. You want the mixture to be very moist but not too soupy. If needed, add more buns to achieve the desired consistency.
Pour the mixture into the prepared dish and bake for about 1 hour, or until sponge like.
While the pudding is baking, melt the butter in a saucepan over medium heat. Whisk in the butter, sugar, cocoa powder and beer. Bring to a light boil for about 2 to 3 minutes, or until the mixture thickens slightly, stirring frequently.
Cut and the pudding into squares and drizzle with the Beer Chocolate Sauce on top. Serve warm.