In a large bowl, combine ground beef, breadcrumbs, onion, heavy cream, egg, salt, and pepper, mixing until just combined.
Divide into 4 portions, shaping into 4 balls, flattening until ½ inch thick, and set aside.
Cook the hamburgers in a nonstick skillet, cooking 4 to 5 minutes per side. Transfer hamburgers onto a clean plate.
In the same pan melt the butter, add onion, cooking on medium heat until golden and softened, about 5 to 7 minutes. Add garlic, cooking until fragrant, about 20 seconds.
Season with salt and pepper; add flour, whisking until the flour lumps have dissipated. Lower the heat to medium-low and add in the stock first, followed by the heavy cream, whisking continuously until it thickens. Whisk in 1 tablespoon of the dill.
Nestle the hamburgers into the sauce and let everything simmer for 4 to 5 minutes. Season again with salt and pepper and garnish with remaining dill. Enjoy!
