In a large bowl, combine ground beef, beaten egg, breadcrumbs, salt, black pepper, and shallots. Mix gently until just combined. Shape into four patties and let rest for 20 minutes.

Heat a skillet over medium-high heat with olive oil and butter. Sear patties for 5 minutes on each side until cooked through. Remove and keep warm.

Lower heat and add minced garlic and remaining shallots to the skillet. Sauté for about 1 minute until fragrant.

Stir in yellow mustard, pinch of salt and pepper, and flour. Cook for 1 minute until it forms a roux.

Pour in whiskey, scraping up browned bits. Stir for 3 minutes as it simmers.

Add beef broth and bring to a gentle boil. Stir in cream and simmer for 2-3 minutes until slightly thickened.

Return the patties to the skillet, spoon sauce over them, and simmer for an additional 5 minutes on low.

Garnish with chopped chives and serve with sides like mashed potatoes or crusty bread.