1/4 onion sliced very thin 1 tablespoon oil 3 tablespoons butter 1/2 cup cream Salt and pepper to taste 1 tablespoon balsamic vinegar 1 pound chopped beef round 1 cup freshly grated Parmigiano-Reggiano® 2 egg yolks
In a skillet sauté the sliced onion in the vegetable oil and 1 tablespoon butter. When the onion becomes a light gold color, add the cream, salt, pepper and the balsamic vinegar and stir thoroughly. Reduce the cream, then turn off the heat, allowing the sauce to cool for 1 to 2 minutes. Set aside.
Combine the chopped beef, the grated Parmigiano-Reggiano and the egg yolks. Mix very thoroughly, correct for salt and pepper and shape into 6 patties. Brown them in a pan with 2 tablespoons butter. Transfer to a warm platter pouring the sauce over the patties and serve.