Prepare the asparagus by snapping off the tough, woody ends. If desired, use a peeler to remove about 2 inches of peel from the stalk. Fill a wide, deep skillet with water and place over high heat to bring to a boil.
In a small saucepan melt the unsalted butter. Let sit for a few minutes to separate. Scoop off the white foam on top of the butter. Slowly pour the melted butter into a container, stopping when you reach the milk layer on the bottom. Melt and add more butter to make sure you have at least 1 cup of clarified butter.
Fill a sauce pan with about 1 inch of water and place over medium low heat. Bring to a very gently simmer. Use a rasp to zest the blood orange and set aside. Juice the blood orange, straining to remove any pith or seeds. Fill a small glass with cold water and have nearby the stove.
Place the egg yolks into a clean mixing bowl. Add the lemon juice and 1 tablespoon of the blood orange juice. Whisk together. Place the bowl over the simmering water. Turn the heat down so it is barely bubbling. Whisk the egg yolk mixture constantly while making the sauce.
Continue whisking the egg yolks for 1 minute until they begin to thicken slightly. Begin adding the clarified butter a few drops at a time while continuing to whisk. Slowly drizzle in about half of the butter while whisking.
If it begins to look like the butter is separating out from the sauce, quickly add a few drops of cold water and whisk it back together. On the other hand, if the sauce begins to look curdled or like it is going to scramble, remove from the heat immediately and finish making the sauce off of the heat.
Add another tablespoon of the blood orange juice and whisk together. Continue drizzling in the butter, while whisking, until all of the butter has been incorporated. Remove the bowl from the heat and add the kosher salt, blood orange zest, and the remaining blood orange juice. Whisk together and taste the sauce. Adjust the seasoning if needed. Set aside while blanching the asparagus.
Bring the water in the skillet to a boil and add a good amount of kosher salt. Taste the water - it should taste well seasoned. Add the asparagus and cook for 4 to 5 minutes until crisp tender. Remove the asparagus to a paper towel lined plate to drain.
Arrange the asparagus on a serving platter. Spoon the maltaise sauce generously over the asparagus. Garnish with more blood orange zest if desired. Serve with any extra sauce on the side and enjoy!