Steak Diane for Two

beef fillets, cut from the tenderloin (filet mignon), preferably not too lean

Salt and pepper

extra-virgin olive oil

butter

minced shallot or onion

Dijon mustard

Worcestershire sauce, or to taste

heavy cream or half-and-half

Lemon juice, to taste (optional)

Chopped fresh chives or parsley leaves, for garnish