The key to making a dark roux, as is used in Cajun cooking, is stirring, scraping, and homogeneity. You can crank the heat on high and stir for about 10-15 minutes, or you can keep it over medium and stir for an hour. If you stir like you're supposed to, you can get the same roux in less than half the time. A good wooden spoon (soft enough to scrape the bottom of the pot) that can get into the corners of a pot and a little elbow grease is all you need.
So why do they tell you that you need to stir for so long? Because if you screw it up, you've gotta start over.
I was curious how fast I could do a dark roux (notably, after burning my first one and needing to restart), and I actually managed one in under 8 minutes, and even took a photo to document such:
And yeah, the key really is stirring constantly, and riding the stove knob to keep the heat right.
My stupid thing that I do that sometimes burns it is stopping stirring when I turn off the heat when I'm done. Pan is still hot enough to burn it, if you don't get it out of there, or add vegetables quickly.
The funny thing is that the jarred stuff is just as good as the roux you make on your stove. It's also perfectly fine to make a giant batch of the stuff and freeze it, and there are numerous recipes for doing it in your oven or even your microwave with great results.
The key to making a dark roux, as is used in Cajun cooking, is stirring, scraping, and homogeneity. You can crank the heat on high and stir for about 10-15 minutes, or you can keep it over medium and stir for an hour. If you stir like you're supposed to, you can get the same roux in less than half the time. A good wooden spoon (soft enough to scrape the bottom of the pot) that can get into the corners of a pot and a little elbow grease is all you need.
So why do they tell you that you need to stir for so long? Because if you screw it up, you've gotta start over.