1. Prepare the Stuffing

• In a bowl, combine crab meat, breadcrumbs, mayonnaise, Dijon mustard, lemon juice, Worcestershire sauce, and parsley.
• Mix gently to avoid breaking up the crab. Season lightly with salt and pepper.

2. Prepare the Beef Tenderloin

• Butterfly the tenderloin by slicing lengthwise down the center without cutting through completely.
• Open it like a book, cover with plastic wrap, and pound lightly to an even thickness.
• Spread the crab mixture evenly over the beef, leaving a small border.
• Roll tightly and secure with kitchen twine every 2 inches.

3. Sear and Roast

• Preheat oven to 400°F (200°C).
• In a large oven-safe skillet, melt butter over medium-high heat.
• Sear the tenderloin on all sides until golden brown, about 2–3 minutes per side.
• Transfer to the oven and roast 25–30 minutes, or until internal temperature reaches 135°F (medium-rare).
• Rest for 10 minutes before slicing.

4. Make the Béarnaise Sauce

• In a small saucepan, combine vinegar, shallots, and tarragon. Simmer until reduced by half.
• Strain and whisk the reduction into egg yolks over a double boiler.
• Slowly drizzle in melted butter, whisking constantly, until thick and creamy.
• Season with salt and pepper to taste.

5. Assemble and Serve

• Slice tenderloin into 1-inch medallions.
• Spoon warm béarnaise sauce over each serving.
• Garnish with extra tarragon or a light sprinkle of lemon zest.