Preheat oven to 350 degrees F.
Pat the steaks dry and season all over with salt, pepper, and onion powder. Melt the butter in a cast-iron skillet (or oven-safe skillet) over medium-high heat. Place the steaks in the skillet and cook for 1-2 minutes on each side to get a nice sear. Transfer the skillet to the preheated oven and cook for 6-7 minutes until the steaks are medium-rare (125F internal temp).
While the steaks are cooking, add the white wine vinegar, white wine, and shallots to a small saucepan. Place over medium heat and bring to a roaring simmer. Cook until the liquid has reduced to 2 tablespoons. Strain the liquid to remove shallots. Set aside.
Once the steaks are done, remove them from the oven and transfer them to a plate. Cover with foil and rest for 10 minutes. Return the skillet to the ovena nd turn off the heat. (You're keeping it warm for later.)
Set up a double boiler (see note) to make the sauce. Add the egg yolks to the bowl and immediately start whisking (do not stop whisking at any point). Pour in the strained vinegar and mix. Add one piece of cold butter to the sauce at a time, waiting to add the next piece until the first is almost completely melted. The sauce should thicken and be smooth. Remove from the heat and place the bowl on a kitchen towel. Whisk in the lemon juice to combine. Add salt to taste. Set aside.
Carefully take the skillet out of the oven and toss in the asparagus along with 1 TBSP butter. Turn the asparagus to coat in butter and pan juices. Cook for 5 to 7 minutes until tender and bright green. Season with salt and pepper to taste.
Assembly: Arrange half of the asparagus on a plate. (see note) Top with a steak and arrange half of the crab over the steak. Whisk the sauce and then spoon a generous amount over the crab and steak. Garnish with chopped parsley. Serve extra sauce on the side.