Preheat the oven to 425 degrees.
Toss the sweet potato, brussels sprouts + onion with the olive oil, sea salt + pepper, then arrange evenly in a single layer on a sheet pan. Bake at 425 degrees for about 20-25 minutes, tossing the veggies halfway through.
While the veggies are roasting, bring 2-3" of water up to a boil in a small saucepan over high heat. Stir in vinegar + reduce the heat to medium to bring the water down to a simmer.
Crack an egg into a small ramekin + hold directly over the surface of the simmering water, gently sliding the egg into the saucepan. Let the egg cook for 3 minutes, then remove with a slotted spoon + repeat with the other eggs.
Lastly, make the hollandaise sauce by blending the egg yolks, lemon juice + sea salt in the blender. With the blender still running, slowwwwly drizzle the hot melted butter in through the feeder hole in the blender lid. It will thicken up into a sauce immediately. Season further as needed + serve immediately.
To serve, place the roasted veggies in two bowls, top with the eggs + hollandaise, then garnish with minced parsley.