Start by placing the breadcrumbs into a large mixing bowl. Using the fine side of a box grater, grate the onion directly over the breadcrumbs. This technique allows the onion’s moisture to hydrate the breadcrumbs. Gently mix with your fingers and let it sit for a few minutes.

Add the ground beef, minced garlic, egg, ketchup, crumbled bouillon, Worcestershire sauce, and mustard into the bowl. Use your hands to thoroughly combine the mixture, kneading for a couple of minutes until it becomes slightly sticky and cohesive. This ensures the patties will hold together during cooking.

Divide the mixture into five equal portions and shape each into a firm oval patty, about 3/4 inch (1.6 cm) thick.

Heat the olive oil in a large skillet over high heat. Once shimmering, carefully add the beef patties. Sear the first side for about 1 minute or until browned, then gently flip to brown the other side. The insides will still be undercooked at this stage. Remove the patties and set them aside on a plate.

If the skillet appears dry, drizzle in a bit more oil. Add the chopped onions and garlic, and sauté for about 2 minutes until fragrant and beginning to soften.

Toss in the mushrooms and continue to cook for another 2–3 minutes until they turn golden brown and release their moisture.

Reduce the heat to medium and add the butter to the pan. Once melted, sprinkle in the flour and stir constantly for about 30 seconds to form a smooth roux.

Gradually pour in the beef broth while stirring to prevent lumps from forming. When the mixture is mostly smooth, whisk in the water, Dijon mustard, and Worcestershire sauce. Keep stirring until fully combined.

Gently return the partially cooked steaks to the skillet along with any juices collected on the plate. Let everything simmer together for 5–7 minutes, or until the patties are cooked through and the gravy thickens. Stir occasionally, focusing around the edges of the steaks. If the sauce becomes too thick, splash in a little extra water.

Remove the steaks from the pan. Taste the gravy and adjust with salt and pepper as needed.

To serve, plate the steaks and generously ladle the savory mushroom gravy over the top. They’re perfect over a bed of creamy mashed potatoes and can be finished with a sprinkle of chopped parsley for a touch of color.