01 - Preheat the 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 and sprinkle with kosher salt and black pepper. Toss to coat evenly.
03 - Roast the asparagus for 12 to 15 minutes until tender and lightly browned, shaking the pan halfway through cooking.
04 - Whisk egg yolks and lemon juice in a heatproof bowl set over simmering water (double boiler) until slightly thickened.
05 - Gradually whisk in warm melted butter until the sauce is thick and glossy. Stir in Dijon mustard if using, cayenne pepper, and salt to taste. Remove from heat immediately.
06 - Arrange roasted asparagus on a serving platter and spoon Hollandaise sauce generously over top. Serve immediately.