Mix de coffee powder with the sugar, salt, and pepper. Mix the ground beef with most (but not all) of the chopped onion, and the egg yolk. Add breadcrumbs until it is one solid mass.

Make two burger out of the meat and cover it entirely with the coffee mix. Then cook it for a few minutes on both sides. It will look burnt because of the coffee, but it isn't. In the mean while slice the other halve onion into rings, and cook them with the burger.

For toppings you slice the tomato and lettuce. Then, after placing the meat on the two buns, add all the vegetables. You can use the remainder of the lettuce, tomato and chopped onion for decoration of the plate.

For the sauce you have three possibilities. First, some (hot) salsa/dip sauce. Second, mix the mayonnaise with the remainder of the coffee mix. Third, mix the mayonnaise with paprika powder, very little chili powder, salt and pepper. All three are delicious and you should try them. Don't forget one of the sauces for on the decoration.