In a large bowl, combine the ground beef, breadcrumbs, salt, coarsely ground black pepper, egg, and grated shallots. Mix gently until just incorporated.

Divide the meat mixture into four equal portions and shape them into patties about ¾ inch thick.

Heat a skillet over medium-high heat with olive oil and unsalted butter. Sear each patty for about 5 minutes until golden brown.

Lower the heat, add the diced shallots and minced garlic, stirring until fragrant.

Stir in yellow mustard, additional salt, pepper, and flour, cooking for 1-2 minutes to create a roux.

Deglaze the pan with whiskey and allow to cook for another minute.

Add the beef broth and bring to a gentle boil, simmering for about 2-3 minutes. Stir in heavy cream.

Return the seared patties to the skillet and simmer in the sauce for an additional 5 minutes.

Remove from heat and garnish with chopped chives. Serve hot.