In a large bowl, gently mix ground beef, breadcrumbs, beaten egg, finely diced onion, salt, and black pepper until just combined. Be careful not to overwork the mixture.

Form the mixture into 6–8 oval-shaped patties that feel slightly firm but tender. Let them rest while you heat the skillet.

Heat an oven-safe skillet over medium-high heat. Brown patties for 3–4 minutes per side until they've developed a deep golden crust. Remove from the skillet and set aside.

Reduce heat to medium and add butter to the same skillet. Add the sliced onion and sauté until soft and fragrant (about 5–6 minutes), stirring to loosen the fond.

Sprinkle in the flour and stir constantly for 1–2 minutes until you smell a toasty aroma.

Slowly whisk in the beef broth, then the heavy cream; allow the gravy to thicken. Stir in the garlic powder and adjust seasoning to taste.

Nestle the browned patties back into the gravy, spooning sauce over each to keep them moist.

Cover the skillet tightly and bake in a preheated oven at 350°F for 45 minutes until patties are tender and the gravy bubbles gently.

Uncover and bake for an additional 15 minutes to reduce the gravy slightly and brown the edges.

Remove from the oven and let rest for 10 minutes before serving.