Spoon the condensed milk into the base of a small heatproof glass.
Add a strip of lemon peel and pour the liqueur gently over the back of a bar spoon so it sits above the milk.
Pull an espresso and pour it slowly down the spoon to form the third layer.
Top with hot foamed milk.
Dust with cinnamon and serve without stirring — the layers are the point until the drinker breaks them.
Native to Tenerife, where ordering one "completo" gets you all four layers plus the lemon and cinnamon. The lemon peel is not garnish: it sits in the liqueur layer and perfumes it from below.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Barraquito.