In a large bowl, combine the ground beef, breadcrumbs, egg, grated onion, garlic powder, salt, and black pepper. Mix just until combined, then shape into 4 oval patties.
Heat olive oil in a large skillet over medium-high heat. Sear the patties for about 3–4 minutes per side until beautifully browned. Remove them from the skillet and set aside (they will finish cooking in the sauce).
Reduce the heat to medium and add the butter to the same pan. Sauté the sliced mushrooms and chopped onions for 4–5 minutes until soft and golden. Stir in the minced garlic and cook for 1 more minute.
Pour in the beef broth, scraping up any delicious browned bits from the bottom of the pan. Stir in the heavy cream and the coarsely crushed peppercorns. Bring to a gentle simmer.
Return the beef patties to the skillet, spooning the sauce over them. Simmer uncovered for 8–10 minutes until the gravy is thick and glossy, and the steaks are tender and fully cooked through.
Plate hot, heavily smothered in the creamy mushroom gravy. Pair it with mashed cauliflower or roasted veggies for a perfect low-carb meal!
