- 2 Tbs. unsalted butter
- 1/4 cup minced shallot
- 1/2 cup Cognac
- 3 cups unsalted or lower-salt chicken stock or broth
- 4 small sprigs fresh thyme
- 2 cups heavy cream
- 2 tsp. freshly cracked black pepper
- 1/4 oz. finely grated Parmigiano-Reggiano (1/4 cup using a rasp grater)
- 2 tsp. Dijon mustard
- 2 tsp. fresh lemon juice; more as needed
- 2 tsp. Worcestershire sauce
Melt the butter in a 3-quart saucepan over medium-low heat. Add the shallot and cook, stirring occasionally, until tender, about 3 minutes.
Add the Cognac, turn the heat up to high, and boil until reduced by half, 2 to 3 minutes. Add the stock and thyme and boil until the mixture has reduced to just over 1 cup, 15 to 20 minutes. Discard the thyme sprigs.
Stir in the cream and black pepper and lower the heat to maintain a gentle boil. Cook, stirring occasionally, until the sauce is reduced to 2 cups and is a bit thicker than heavy cream, about 20 minutes.
Remove from the heat and whisk in the Parmigiano, mustard, lemon juice, and Worcestershire sauce. Once the cheese has melted, season to taste with more salt, pepper, or lemon juice.