Finely chop the onion and set aside.
Melt butter in a pan and sauté the onions.
In a bowl, combine ground beef, pork, sautéed onions, breadcrumbs, egg, salt, and pepper. Mix well.
Shape the mixture into hamburger steak patties.
Heat oil in a pan and cook the hamburger steaks on both sides until golden brown.
In the same pan, add butter and lightly sauté flour, then add water, ketchup, Worcestershire sauce, and sugar. Bring to a boil.
When the sauce thickens, pour it over the cooked hamburger steaks to finish.