Heat the oven to 375°F. Line a 9×5-inch or 10×5-inch loaf pan with parchment paper (if your pan isn't non-stick, grease any inside ends if they're exposed). Note, if you only have an 8.5×4.5-inch loaf pan, you'll need a small additional vessel, as you definitely don't want to over-fill the loaf pan---it will spill over!

In your stand mixer, cream the butter, sugar, and zest for around two minutes, until light and fluffy. Add the eggs and vanilla and beat to combine. You can add a tablespoon or two of flour if it looks like it's going to curdle.

Then fold in the melted, slightly cooled chocolate. Blend well, but don't overmix. Add the coffee and alcohol and mix just to combine.

Finally, add the dry ingredients and mix only until they're absorbed. The batter should be fairly smooth and will be quite liquid (mine always has some clumps, but they haven't been an issue).

Pour into the loaf pan, making sure the batter does not come closer than 1 inch from the rim.

Bake for 30 minutes at 375°F, then turn the oven down to 325ºF and continue to cook for another 15 to 20 minutes more (mine took even a bit more, since I did it all in one pan). If you're baking the leftover batter in a small pan, remove after the first 30 minutes.

The cake may still be a bit squishy and a skewer may not come out entirely clean, but it should be close. Remove from the oven and place on a rack to get completely cool before turning out. Even a full day is okay, this is actually great made the day before. It will sink in the middle, this is totally normal!

Slice and serve with just a sprinkle of powdered sugar, or a light whipped mascarpone cream.