In a small saucepan, combine the egg yolks, sugar, flour, vanilla, and espresso. Whisk until well combined. Add a bit of milk and turn the heat to medium-high, stirring continuously with a wooden spoon. Bit by bit, add the milk to the egg mixture, being sure to keep stirring so as not to let the eggs begin to cook at the bottom edges of the pan. Once all the milk has been added, bring to a boil then reduce to a gentle simmer, stirring all the while. Keep sitting until the mixture thickens. Remove from the heat and let the cream cool.
In a separate bowl or the bowl of an electric mixer fitted with a whisk, mix the cream until it forms thick whipped cream. Using a spatula, gently fold 2/3 of the whiped cream into the egg custard mixture. Separate the custard into 6 tall glasses. Chill the filled custard glasses in the refrigerator for 1 hour. Just before serving, top each glass with a spoonful of the remaining whipped cream and a coffee bean.