Add 2 tbsp unsalted butter to the searing pan and heat over medium heat until butter melts. Add 1/2 lb chanterelle mushrooms or 1/2 lb of sliced cremini mushrooms to the pan and season with kosher salt and freshly ground black pepper. Sauté until the mushrooms release their moisture and turn golden, about 5-7 minutes. Remove the mushrooms from the pan and set aside on a plate.
Add 1 medium diced shallot to the remaining butter in the pan and sauté until the onions turn golden brown on the edges and the onions become soft, about 3-5 minutes]. Add 1-2 cloves grated garlic, stir and let the mixture sizzle for a minute or until the garlic becomes fragrant. Add 1 tsp dried thyme or 4-5 sprigs fresh thyme and stir to combine.
Remove the pan from heat and stir in 1 tbsp bourbon or cognac and deglaze the pan, scraping up the brown bits from the bottom of the pan.
Return pan to heat and stir in 1/2 tsp Dijon mustard, 1 tsp Worcestershire sauce and 1/2 cup beef stock and reduce by 1/3 to 1/2. Stir in 1/4 cup heavy (whipping) cream and season with kosher salt and freshly ground black pepper.