
Trim all excess fat chunks off the steaks. Then finely chop the filets into ¼ inch pieces. Do this by cutting the steaks into fine strips. Cut the strips in halves or thirds. Then cut the steak ribbons crosswise.
Mince the shallots and capers. Zest and juice the lemon. In a measuring cup, add the egg yolk, 1 tablespoon lemon juice, and spicy mustard. Stir to combine.
Set out a mixing bowl. Add the chopped steak, minced shallots, capers, egg yolk mixture, parsley, olive oil, lemon zest, 1 teaspoon salt, and ½ teaspoon cracked black pepper. Mix well.
Taste, then add additional salt, pepper, or lemon juice if desired.
Serve immediately. For traditional plating, press the steak tartare into ramekins, then flip it out onto small serving plates in the shape of a disk. Garnish with extra parsley and/or capers. You can also rest an extra egg yolk on top, but be aware this will make the tartare texture extra dense and silky.