A perfect espresso has many things in common with a perfect roux, not the least of which is the dark nutty brown color that defines success in each. My father, a New Orleans native, has a gentle way of telling you that your roux sucks. When you ask his opinion of your raw undercooked roux he reassuringly tells you that you've created a "nice blond roux" -- which makes it sound like it's a "thing". It's not a thing. A blond roux means it's raw and undercooked. The same goes for espresso, if your espresso is anything other than the deep brown hue of a hazelnut you probably shouldn't serve it.
|THIS is an espresso.|
|THIS is a roux.|