I have found I enjoy sauteed mushrooms and grilled onions on burgers. Add in some muenster and bread and butter pickles on a toasted sesame seed bun, and great I just made myself hungry for one.
Sauteed mushrooms go well with the burgers. Their savory, almost meaty taste enhances the savory taste of the beef, especially when paired with a gravy. Together, they are the "flavor bomb" full of intense umami.
Grilled onions are okay despite the uneasiness. They have a sweet, almost smoky taste that balances the richness of the beef patty - and are better than the raw onions that have a much sharper bite. They are not something I would specifically order, but I would not discard them if I found them on my burger.
Muenster is a very delicious cheese, and it melts 75% as well as the American cheese so long as it's not overcooked. It makes for a nice golden melted coating, filling in the nicks and crannies of the meat patty. The taste is almost buttery and has a mild, not overpowering taste. It matches well with the savouriness of the sauteed mushrooms and beef and the sweetness of the grilled onions. It is like the glue that harmonizes all the flavors together.
Sesame seed buns are popular here too. They were popularized by the McDonalds as part of their Big Mac campaign 40+ years ago. It is very visually appealing and adds the "class" to an otherwise plain bun as well imparting it a faint nuttiness. Toasting the buns improves the burger texture as a whole, giving much needed crunchiness to otherwise very soft textures.
The sourness of butter pickles helps cut the richness of the beef and also provides freshness and crunchiness. It helps break down the monotony of having the same strong savory flavors over and over and gives the taste buds something else to focus on.
I really like your burger. It has a lot of elements that go well together. Biting into one would have a nice crunchy and soft texture, and chewing on it would bring a multitude of complementary flavors.
Do you prefer a thicker patty burger or do you prefer the smashburgers?