Combine heavy cream, buttermilk, and half of sugar in a medium sized sauce pot. Set over medium heat and bring to a simmer.
Meanwhile, in a medium bowl whisk together remaining sugar and egg yolks. Slowly pour the hot liquid mixture over the yolk mixture, whisking constantly to distribute the heat. Mix well, then pour mixture back into sauce pot.
Set pot over medium heat. Using a wooden spoon or spatula, gently stir the mixture making sure to pay attention to the bottom and sides of the pan as to not burn the yolks. Continue to stir and heat the mixture until it reaches nappe consistency (thickens and coats the back of a spoon), or until it reaches a temperature of 180 degrees F on a thermometer. Remove from heat and add in espresso powder and salt. Stir until dissolved.
Cool mixture over an ice bath. Alternatively, pour mixture into a plastic wrap lined sheet tray. Spread over the sheet tray and cover with plastic wrap. Let cool in the freezer for 5-10 minutes until mixture has cooled to room temperature. Transfer cooled mixture into an airtight container and let mature in the fridge overnight.
Freeze mixture in ice cream maker according to your unit's instructions. Once the volume has increased by 1/2 and mixture has reached a soft-serve consistency, about 20-25 minutes, turn off machine. Transfer 1/3 of ice cream into an airtight, freezer-safe container. Drizzle a heaping tablespoon of melted caramel sauce over ice cream. Spread another 1/3 of ice cream into container and drizzle with caramel. Add remaining ice cream on top and drizzle with remaining caramel. Cover container and let rest in the freeze for at least 1 hour before serving.
Let ice cream sit out for 5 minutes before scooping. Serve with additional caramel sauce and a sprinkling of cacao nibs for crunch.