Place whole black peppercorns in a zip-top bag
Lightly crush using a rolling pin or skillet until coarsely cracked
Heat butter and olive oil in a skillet over medium heat
Add chopped shallots and sauté for 2–3 minutes until soft
Stir in cracked peppercorns and cook for 30–60 seconds
(Optional) Add brandy or cognac and cook for 30 seconds to burn off alcohol
Pour in beef broth and scrape up browned bits from the pan
Simmer for 3–4 minutes until slightly reduced
Reduce heat to medium-low
Stir in heavy cream, Worcestershire sauce, and Dijon mustard
Simmer gently for 5–7 minutes, stirring frequently
Taste and season with salt as needed
Remove from heat once sauce coats the back of a spoon