Begin by dicing the yellow onion and mincing the garlic. In a large bowl, combine ground beef, egg, breadcrumbs, dried onion, Dijon mustard, salt, and black pepper. Use clean hands to mix gently until just combined, ensuring not to overwork the meat mixture.

Divide the meat mixture into four equal portions and shape each into a patty about ¾-inch thick. Make a slight indentation in the center of each patty to help them cook evenly.

Heat a large skillet over medium-high heat and add a mixture of olive oil and unsalted butter. Sear the patties for about 5 minutes on each side until they develop a rich, golden-brown crust.

Lower the heat to medium and sauté the diced onion and minced garlic in the skillet for about 3 minutes. Deglaze the skillet with dry white wine and cook for an additional 2 minutes.

Pour in the heavy cream and bring the mixture to a gentle boil. Stir in the grated Parmesan and horseradish, adjusting the horseradish to taste. Return the cooked Salisbury steaks to the skillet and simmer for about 5 minutes.

Remove from heat, serve the Salisbury steaks warm, garnished with chopped chives, and enjoy!