The best hamburger you can find in Madrid (at least I think) in a 60's ambience. It seems to eat in a volkswaken mini bus with soft lights seated in comfortable couches.
You have a huge choice of hamburgers: veggie, traditional. chicken, etc. I've tried a classic cheeseburger: the meat was soft, tasty and natural, all the ingredients fresh, the french fries very good and the service friendly.
There's a Home Nurger Bar at Tribunal Metro Station and one in Chueca.