Step 1

Sauté onions in oil over medium heat until golden brown, about 5 minutes.

Step 2

In a large bowl, combine half of the sautéed onions, ground beef, ground turkey, bread crumbs, egg, egg white, 1/4 cup beef broth, salt and black pepper. Shape into 8 oval patties.

Step 3

In a large deep skillet over medium-high heat, brown both sides of patties, about 4 to 5 min on each side, in batches as needed. Set aside on a dish.

Step 4

Add mushrooms to the skillet, season with salt and pepper and sauté 2-3 minutes.

Step 5

Return patties to the skillet with the mushrooms.

Step 6

In a small bowl, blend flour and remaining broth until smooth. Mix in remaining onions, tomato paste, vinegar, water, worcestershire sauce and mustard powder. Pour over meat and mushrooms in skillet.

Step 7

Cover and cook on low heat for 20 minutes, stirring occasionally.