Step 1

Mince 1 large shallot. Finely chop 1/2 bunch fresh chives until you have about 3 tablespoons. Place 1/2 teaspoon whole black peppercorns in a mortar and pestle or spice grinder and coarsely crush. Drain and rinse 1 1/2 tablespoons green peppercorns in brine.

Step 2

Place the shallot, 1 tablespoon of the unsalted butter, and 1/4 of the teaspoon kosher salt in a medium skillet over medium heat. Cook, stirring occasionally, until shallots have softened and are lightly browned at the edges, 2 to 3 minutes.

Step 3

Remove the skillet from the heat. Carefully add 1/2 cup brandy or Cognac. Return to medium-high heat and cook until reduced by half, about 1 minute.

Step 4

Whisk in 1 cup beef stock, green peppercorns, and 1/4 teaspoon of the black peppercorns. Bring to a rapid simmer. Simmer until reduced by half, about 3 minutes.

Step 5

Add 1/3 cup heavy cream and the remaining 1 tablespoon unsalted butter and whisk to combine. Bring to a simmer. Reduce the heat to medium-low and simmer until slightly thickened, 4 to 5 minutes. If you would like an even thicker sauce, mix 2 teaspoons cornstarch with 2 tablespoons water and add to sauce, whisking continuously. Cook for 1 minute more.

Step 6

Add the remaining 1/4 teaspoon kosher salt. Taste and add season with more kosher salt and crushed black pepper as needed. Serve sauce spooned over steak, chicken, or grilled mushrooms. Garnish with the chives.