Start by preparing the chile. Using a sharp knife, carefully slice from the stem end to the bottom end on one side of the chile. Pull off the stem and discard. Open the chile like a book. Using your knife, scrape out the ribs and seeds.
Warm a small skillet over medium heat then toast each side of the chile until very aromatic. Use a spatula to press down on the chile to ensure even toasting (about 10 seconds per side). Place the chile in a small saucepan and cover with half and half. Warm over medium heat until you see steam rising from the surface of the liquid (but not boiling). Cover and let steep for 10 minutes.
Transfer the entire mixture to a blender and process until smooth. Pour the mixture through a medium mesh basket strainer back into the same saucepan, using a spoon to help the liquids pass through. Also gently press on the solids to extract the most liquid. Discard solids.
Prepare an ice bath in a large bowl (ice and water). Set a medium sized bowl in the ice bath and have a fine mesh basket strainer ready. Place a medium sized saucepan filled with 1 inch of water over high heat. Choose a medium sized bowl that will fit snuggly into the saucepan without touching the water. We will be using this bowl below.
Bring the water to a boil. Reheat the half and half mixture over medium heat just until steam rises from the surface. Spread the bittersweet chocolate out in the bottom of a bowl. Pour the half and half mixture over the chocolate, stirring to melt the chocolate.
In the medium size bowl selected above (that will fit in the saucepan), add sugar and egg yolks, whisking until slightly thickened and lighter in color. Slowly whisk in the chocolate mixture. Reduce the heat under the pot of boiling water to a simmer then set the bowl with the custard base (half and half, eggs, sugar, chocolate) on top of the saucepan.
Whisk frequently and scrape down the sides of the bowl with a rubber spatula occasionally until the mixture thickens (about 5 minutes). Test for doneness by dipping a spoon into the mixture. Run your finger down the back of the spoon in a straight line through the custard. If the line holds clearly (and doesn't run), it's done!
Pour the custard through the mesh basket strainer into the bowl sitting in the ice bath and stir until cool. Refrigerate for at least for 4 hours (preferably overnight). Stir in heavy cream, vanilla extra and coffee liqueur.
Freeze custard in an ice cream maker according to the manufacturer's instructions. Finish by freezing the ice cream until hard or enjoy soft immediately.
If you want to bump up the heat level a bit, serve with a dusting of cayenne pepper.