Step 1: Prepare the Beef Tenderloin

1. Season the Beef: Rub the beef tenderloin with olive oil, then season it generously with salt, black pepper, garlic powder, and smoked paprika. Let the meat rest at room temperature for 20 minutes to ensure even cooking.
2. Preheat the Grill: Heat your grill or grill pan to medium-high heat. Lightly oil the grates to prevent sticking.
3. Grill the Tenderloin: Sear the beef for 3-4 minutes on each side to develop a golden-brown crust. For medium-rare, grill until the internal temperature reaches 135°F. Remove the tenderloin from the grill, cover loosely with foil, and let it rest for 10 minutes before slicing thinly.

Step 2: Make the Crostini

1. Prepare the Bread: Arrange the baguette slices on a baking sheet. Brush both sides with olive oil.
2. Toast the Bread: Preheat your oven to 375°F (190°C). Bake the slices for 7-9 minutes, flipping halfway through, until golden and crisp.
3. Add Flavor: While the bread is still warm, rub each slice lightly with the cut side of a garlic clove for subtle garlic flavor.

Step 3: Make the Béarnaise Sauce

1. Start the Reduction: In a small saucepan, combine white wine vinegar, white wine, shallots, and tarragon. Bring to a simmer over medium heat and reduce until about 2 tablespoons of liquid remain. Strain and set aside to cool slightly.
2. Prepare the Egg Yolks: In a heatproof bowl, whisk together the egg yolks and the cooled reduction. Place the bowl over a pot of simmering water (double-boiler method), ensuring the bottom doesn’t touch the water.
3. Emulsify the Sauce: Slowly drizzle in the melted butter while whisking constantly. Continue whisking until the sauce thickens to a silky consistency. Remove from heat and stir in salt, black pepper, and lemon juice. Keep warm until ready to serve.

Step 4: Assemble the Crostini

1. Layer the Ingredients: Place a slice of grilled beef tenderloin on each crostini. Spoon a dollop of Béarnaise sauce over the top.
2. Garnish: Sprinkle with chopped tarragon or parsley and a pinch of cracked black pepper for a finishing touch.