First prepare the hamburgers normally. To do this, fry the patties, bake the buns briefly and spread with mayonnaise. Wash the lettuce and prepare large leaves, slice the tomatoes.
For the sauce, cut the onion into strips and sauté in a little oil until glassy to yellow, then deglaze with the beer and boil down until half of the beer is reduced. Then add tomato paste and ketchup and boil up or reduce again.
The sauce should have a thick consistency. Then top the burgers as desired with the ingredients and the sauce on top. You can also add crispy bacon or fried onions.
You can also switch the type of beer to get a different flavor in the sauce – Krefelder (black beer + cola) creates a smokier note.