In a large heatproof bowl, microwave the unsweetened chocolate at 50% power in 1 minute intervals, stirring in between, until completely melted. Set aside to cool.
In a 2-cup liquid measuring cup, combine the espresso powder and cocoa powder. Add to it the boiling water and stir until dissolved.
Add the bourbon, cinnamon, cayenne pepper, and salt, stirring until well blended. Set aside to cool.
Preheat oven to 325 degrees Fahrenheit.
Grease and flour (or spray baking spray) evenly a 10-cup bundt pan and set aside.
In the bowl of a stand mixer, cream the butter and sugar on low/medium-low speed until light and fluffy. DO NOT RUSH THIS STEP.
Beat in the eggs, one at a time, waiting until the first is fully incorporated before adding the next.
Add the vanilla extract and baking soda, beating until incorporated.
While the mixer is on low/medium-low speed, pour the melted chocolate into the bowl. Scrape the sides as needed to mix fully.
Continue mixing, pouring in 1/3 of the espresso/cocoa powder/bourbon liquid. Mix until incorporated.
Add 1 cup of flour and mix until incorporated. Stop and scrape sides of the bowl as needed.
Pour in 1/2 the remaining liquid, mixing until incorporated. Repeat with the remaining 1 cup of flour, and then the last of the liquid.
Remove bowl from mixer and stir in the chocolate chips.
Pour into prepared bundt pan and bake for 1 hour 10 minutes, or until the top springs back when lightly touched. (If you're concerned about overflowing, you can put a parchment-lined baking sheet on the rack below the bundt pan.)
Cool on wire rack for 15 minutes.
Run a butter knife around the edges of the pan and then invert onto the wire rack. If the cake does not release easily, let it cool for another 5-10 minutes before trying again.