In a mixing bowl whisk the eggs and egg yolk until combined. Add the brown sugar, vanilla, espresso powder, salt, coffee, and whiskey. Then whisk in the milk until all is blended.
In a mixing bowl add the bread cubes, pour the egg mixture on top, and toss until all is coated. Cover and refrigerate for an hour to allow the bread to absorb all of the milk mixture.
Preheat the oven to 350°F, 177°C, or gas mark 4.
Pour the soda bread into the seasoned cast iron skillet. Bake for 35 minutes. Allow to cool before serving.
Making the caramel sauce
In a saucepan on medium-high heat add the sugar and water. Stir to dissolve the sugar. Once the sugar is dissolved stop stirring. This could cause the caramel to seize. Allow to boil undisturbed until the caramel starts to take on a rich amber color. To mix gently swirl the saucepan. Once all of the sugar has started to change to a caramel color.
Add the cream and this will cause a violent bubbling reaction, just keep stirring. After the caramel boiling has reduced remove from the heat and add all but 2 tablespoons of the whiskey. This will boil violently again as the alcohol cooks out. Return to the heat and cook for 2 minutes.
Once the caramel sauce has started to thicken remove from the heat again. Once the sauce is almost to room temperature, add the remaining whiskey and whisk until combined.