In a bowl, blend the ground beef, onions, garlic, salt and pepper and mix well.
Next, by hand, portion the meat into 8 to 9 round patties, ensuring they are not more than 1/4-inch tall. Next, heat a large saucepan with the oil over medium-high heat. Add the seasoned patties, allowing to cook on each side until browned, 3 to 4 minutes. After browning both sides, finish in the oven for 4 to 5 minutes for medium-well. Remove from the oven.
After baking, remove the patties from the pan and hold on the counter; this will allow the meat to rest. Then, return the pan to medium-high heat for 2 minutes. After the pan is hot again, carefully add the brandy and allow the liquor to cook off. Then add the stock, mushrooms, herbs and nutmeg and cook for 3 to 4 minutes, allowing the sauce to reduce to 1 cup volume. After reducing the sauce, remove the pan from the heat and whisk in the butter to finish the sauce. Serve with the chopped steak.