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 gently to coat evenly.
03 - Roast asparagus for 12 to 15 minutes until tender and lightly browned, shaking the pan halfway through cooking.
04 - In a heatproof bowl over barely simmering water, whisk egg yolks and lemon juice constantly until slightly thickened.
05 - Gradually whisk in melted butter a little at a time until 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, spoon Hollandaise sauce generously over the top, and serve immediately.