Asparagus with Easy Hollandaise Sauce and Crispy Onions

Preheat oven to 425 degrees F. Line half sheet pan with parchment paper and spread asparagus in a single layer on the parchment. Drizzle with olive oil and season with salt and pepper. In a medium pot filled with 3 inches of oil, heat to 365 degrees F. Meanwhile, line a plate with paper towels. Rinse onions in a bowl of cold water and pat dry on a kitchen towel to remove moisture. Add cornstarch to a mixing bowl and dredge onions. When oil has reached 365 degrees F, shake off excess cornstarch and add onions to hot oil in batches. Use a slotted spoon to carefully lower onions into oil. Fry until golden brown, remove from oil and drain on paper towels. Repeat process for second batch and season immediately with salt. After preheating oven, roast asparagus until fork tender, 10 to 15 minutes. In a blender add egg yolks, mustard, lemon zest, lemon juice, 1/2 teaspoon salt, and cayenne. Pulse a few times to combine and run blender until mixture is frothy. Either melt butter in a small sauce pan or a microwave proof bowl. While blender is running, pour hot butter in a slow steady stream. (Sauce should be thick. If needed add a splash of water to thin it out.) Serve sauce immediately or place in a glass or metal bowl wrapped in plastic. Place bowl securely on top of another bowl filled with warm water. Pour hollandaise sauce over asparagus and garnish with crispy onions and parsley.