Ingredients
2 heads garlic
3 tablespoons extra-virgin olive oil
1 large egg
4 teaspoons fresh lemon juice
Kosher salt and freshly ground pepper
3/4 to 1 cup vegetable oil
1 center-cut beef tenderloin (3 pounds), trimmed and tied
1 cup each packed fresh dill, cilantro, and parsley leaves
Preparation
Preheat oven to 400°F. Trim tops of garlic by about 1/2 inch; place in parchment-lined foil and drizzle with 1 tablespoon olive oil. Wrap to seal and roast until soft, 1 hour. Unwrap and let cool completely.
Slip garlic cloves out of their jackets and into a blender. Blend with egg, lemon juice, 1/2 teaspoon salt, and 1/8 teaspoon pepper until smooth. With motor running, slowly stream in 3/4 cup vegetable oil until thick and smooth; if too thin, add up to 1/4 cup more oil. Refrigerate in an airtight container at least 30 minutes and up to 3 days; season to taste before serving.
Place beef on a rack set in a rimmed baking sheet; season generously with salt and pepper. Refrigerate, uncovered, at least 4 hours and up to overnight. Preheat oven to 275°F. Pat beef dry; brush with remaining 2 tablespoons olive oil. Transfer to a roasting pan or large ovenproof skillet, such as cast iron. Roast until a thermometer inserted in center reads 125°F for medium rare, 60 to 65 minutes. Tent with foil; let stand 15 minutes.
Finely chop herbs on a large cutting board and spread out in an even layer. Untie roast and roll in herbs, pressing to coat. Transfer to a serving platter, slice, and serve with aioli.
