Preheat oven to 350 F. Prepare a large baking dish by greasing it generously with butter. I used a 4 quart ceramic casserole dish, which had more than enough room for all of the finished bread pudding.
Combine cream and vanilla extract in a sauce pan over medium high heat and bring to a boil. As soon as it starts to bubble, remove from heat and add the 8 ounces of chopped chocolate. Let this sit for 2-3 minutes, and then whisk together briskly until blended.
In a large bowl, beat the eggs well, then beat in 2/3 cup of sugar until just combined. Whisk in the salt, rum, and room temperature coffee. If the coffee is still warm, you can slowly add it in as you whisk, gently tempering the eggs (Basically, you don’t want to accidentally cook the eggs by introducing a hot element too quickly). Whisk the cooled chocolate-cream mixture into the egg mixture.
Place the cubed challah bread in the prepared baking dish, and pour half of the chocolate-egg mixture over top. Add the chocolate chips and stir everything together until all of the bread is just damp. Pour the remaining chocolate-egg mixture over the top of the bread cubes, evenly distributing it. Sprinkle with cinnamon and the remaining one tablespoon of sugar. At this point, you may bake the dessert immediately, or refrigerate for up to two days, covered in plastic wrap.
Bake the bread pudding for 40-50 minutes in the pre-heated oven. Let it sit for 15 minutes before serving. Spoon out generous warm portions, topped with coconut ice cream or spiked coconut whipped cream.
Right before serving, spoon out only the hardened cream into the bowl of a stand mixer fitted with a paddle attachment, leaving behind the separated coconut water (discard or reserve for another use). Add the spiked rum and whip until soft peaks form. Serve immediately.