In a bowl, soak breadcrumbs in milk for 1-2 minutes. Mix in onion, garlic, Worcestershire sauce, Dijon mustard, thyme, rosemary, black pepper, and salt.
Add ground beef and mix gently until combined. Form into four oval patties about 3/4 inch thick.
Chill patties on parchment paper for at least 30 minutes.
Heat olive oil and butter in a skillet over medium-high heat; sear patties on both sides until browned (3-4 minutes each).
Remove patties; sauté onions and mushrooms until softened. Add garlic and flour; stir for about 1-2 minutes.
Gradually add beef broth while stirring until smooth; season with Worcestershire sauce, thyme, rosemary, black pepper, and salt.
Return patties to the skillet; simmer in gravy for another 15-20 minutes.
Serve hot with extra gravy and garnish with fresh parsley.
Helpful Notes:
Nutrition
Serving Size:1 patty with gravy (approximately 200g)