Warm olive oil and butter in a large saute pan on medium low heat. Peel and slice onions into long, thin slices. Drop all of the onions into the pan, add salt and pepper to taste and toss to coat all of the onions in the oil and butter. Leave them alone to caramelize, only stirring occasionally for at least 30 minutes.

Preheat your grill. Mix ground beef and Worcestershire Sauce together in a large bowl. Shape the beef into hamburger patties. I generally make burgers that are 1/3 pound each but do whatever your family prefers. Rub the outsides of the burgers with a thin layer of olive oil, salt and pepper the outsides. Move the burgers to the grill and cook them to your desired temperature. Heat hamburger buns quickly on the grill or in the oven.

Ten minutes before you are ready to build your burgers, add mushrooms to the caramelized onions and toss them to mix and to coat them with oil. Continue to cook them over medium low. The mushrooms will become soft but at the low temperature will not lose all of their moisture and will be juicy and delicious! The onions should have lost all of their punch and only be sweet and soft now - and completely browned.

Build burgers with lettuce, burger, sliced Gouda, caramelized onions and mushrooms.

Eat hot and ENJOY!!