1-Prep Beef: Cut 1 1/2 pounds beef filet into 12 pieces, each 1-by-2 inches. Season with 1 teaspoon kosher salt and 1/2 teaspoon black pepper.

2-Sear Beef: Heat 1 tablespoon salted butter and 1 tablespoon olive oil in a skillet. Sear beef 45 seconds per side. Set aside to cool.

3-Make Duxelles: Finely chop 6 ounces cremini mushrooms (stems removed) and 1 medium onion. Cook in the same skillet with 1 tablespoon minced fresh thyme until dry, about 5-7 minutes. Stir in 1 tablespoon Dijon mustard. Cool slightly.

4-Prep Pastry: Thaw one 17.3-ounce package puff pastry. Dust surface with all-purpose flour. Cut into 12 squares large enough to wrap beef.

5-Assemble: Place mushroom duxelles on each pastry square, top with beef piece. Brush edges with beaten egg white, fold and seal tightly.

6-Finish Prep: Place on parchment-lined baking sheet. Brush tops with beaten egg yolk. Sprinkle with 1 teaspoon sea salt flakes.

7-Bake: Preheat oven to 400°F (200°C). Bake 16 to 18 minutes until golden.

8-Serve: Cool slightly, garnish with chopped fresh parsley. Serve warm with bottled horseradish cream sauce.