01 -
In a medium bowl, combine ground beef, panko breadcrumbs, chopped onion, egg, Dijon mustard, salt, and pepper. Mix thoroughly until ingredients are well incorporated.
02 -
Divide the mixture into 6 equal portions and shape each into an oval patty. Place on a parchment-lined board until ready to cook.
03 -
Heat vegetable oil over medium heat in a large skillet. Cook patties for approximately 5 minutes on each side until browned but not fully cooked. Remove from skillet and set aside.
04 -
In the same skillet, sauté sliced onions over medium heat until softened and golden, about 5 minutes. Add mushrooms and cook until tender, approximately 3 minutes.
05 -
Sprinkle flour over the vegetables and stir to blend evenly. Cook for 1 minute to remove raw flour taste.
06 -
In a small bowl, combine beef stock, tomato paste, Worcestershire sauce, minced garlic, Dijon mustard, thyme, salt, and pepper. Gradually pour into skillet while stirring continuously to avoid lumps.
07 -
Return patties to the skillet. Bring the mixture to a gentle simmer, then reduce heat to medium-low. Cover and cook for 15 minutes, flipping patties halfway through, until cooked through.