01 - Position rack in center and heat oven to 425°F. Line a rimmed baking sheet with parchment paper.
02 - Spread asparagus in a single layer on prepared sheet. Drizzle with olive oil, season with salt and pepper, and toss until evenly coated.
03 - Roast 12 to 15 minutes, turning once halfway through, until spears are tender and tips begin to caramelize.
04 - In a heatproof bowl, vigorously whisk egg yolks with lemon juice until mixture turns thick and pale, about 2 minutes.
05 - Set bowl over barely simmering water without touching surface. Whisk constantly while slowly drizzling in warm butter until sauce thickens and volume doubles, 4 to 5 minutes.
06 - Remove from heat. Season cautiously with salt and cayenne if using. Thin with warm water if needed.
07 - Arrange roasted asparagus on warmed plates. Spoon Hollandaise generously over spears and serve without delay.