Roughly an hour before baking, mash up the bananas, stir in the bourbon, and cover them up. Let them soak, steep, macerate.
Preheat the oven to 350ºF/175ºC.
Prepare a loaf pan by greasing it with butter and dusting it with flour
In a medium bowl, mix the dry ingredients together.
In a large mixing bowl, cream the butter with both of the sugars.
Add the egg to the creamed butter and sugar and beat it in until it's fully incorporated, then mix in the vanilla, sourdough discard, and bourbon bananas.
Fold in the dry ingredients until combined.
Transfer the batter to the prepared loaf pan, leaving an inch of space to prevent overflow. If there's extra batter, fill up a few muffin tins (those take 25-30 minutes to bake).
In a small jar, shake up the cinnamon and sugar to combine it, then sprinkle a generous layer (as much as you'd like) over the loaf prior to baking.
Bake for one hour, checking for doneness with a toothpick.
Once out of the oven, allow the loaf to sit in the pan for 10-15 minutes before turning it out on a cooling rack to cool completely.