Crush the green, black, and pink peppercorns using a mortar and pestle or a spice grinder.
Melt the butter in a saucepan. Once melted, add the flour and whisk together to form a roux. Cook the roux for 2-3 minutes, until it starts to turn a light brown color. Then add the beef stock, whisking until the sauce starts to thicken.
Next, add the crushed peppercorns to the saucepan and continue to whisk until well combined. Cook the sauce for 2-3 minutes, stirring occasionally, to allow the flavors to develop.
Add the heavy cream and brandy to the saucepan. Stir until the sauce is smooth and combined. Cook the sauce for 2-3 minutes, until it starts to thicken again.