• Preheat oven to 375°F (190°C).
• In a bowl, combine crab meat, cream cheese, breadcrumbs, parsley, Dijon mustard, salt, and pepper. Mix well.
• Slice beef tenderloin lengthwise, creating a pocket without cutting all the way through.
• Stuff the pocket with the crab mixture, pressing gently.
• Tie tenderloin with kitchen twine and season the outside with salt and pepper.
• Sear tenderloin in a skillet over medium-high heat until browned on all sides.
• Transfer to the oven and bake for 20-25 minutes until desired doneness.
• Prepare Béarnaise sauce as preferred while the tenderloin bakes.
• Slice tenderloin, plate, and drizzle with warm Béarnaise sauce before serving.

Bearnaise sauce:

• Melt butter in a saucepan over low heat; skim off and discard foam.
• Reduce vinegar and wine with shallots and peppercorns in a saucepan over medium heat until it measures 3 Tbsp. strained liquid, ⏰ 15–20 minutes. Simmer 1-inch water in a saucepan over medium-low heat. Whisk egg yolks and vinegar reduction in a stainless steel bowl. Place bowl over simmering water (don’t let bowl touch water).
• Whisk mixture vigorously until yolks begin to thicken and whisk begins to leave trails, ⏰ 2 minutes. Remove bowl from heat.
• Off heat, whisk in lemon juice. Begin whisking butter into yolk mixture a drop at a time. As the mixture starts to thicken, whisk in remaining butter in a thin stream. If the mixture gets cold, return bowl to pan of simmering water and continue whisking in butter. Whisk in tarragon; season with salt and cayenne. If sauce seems too thick, thin with a little warm water.
• To keep sauce warm, transfer to a heatproof vessel; place in a pan of warm water set over low heat. Stir sauce often to keep smooth.