01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - Arrange asparagus spears in a single layer on the baking sheet. Drizzle with olive oil, then sprinkle with kosher salt and black pepper. Toss to coat evenly.
03 - Roast asparagus for 12 to 15 minutes until tender and slightly browned, shaking the pan halfway through cooking.
04 - In a heatproof bowl over barely simmering water, whisk together egg yolks and lemon juice until slightly thickened.
05 - Slowly whisk in warm melted butter in small increments until sauce is thick and glossy. Stir in Dijon mustard if using, cayenne pepper, and salt to taste. Remove from heat immediately.
06 - Place roasted asparagus on a serving dish and generously spoon the Hollandaise sauce over the top. Serve immediately.