Preheat oven to 350 degrees F. Pat 2 steaks dry with a paper towel and season all over with 2 teaspoons salt, 1 teaspoon black pepper, and 1/2 teaspoon onion powder.
Melt 2 tablespoons unsalted 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 reach medium-rare (125°F internal temp).
While the steaks are cooking, add 1/4 cup white wine vinegar, 1/4 cup dry white wine, and 1 large shallot 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 oven and turn off the heat. (You're keeping it warm for later.)
Set up a double boiler (see note) to make the sauce. Add 3 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 the cold salted 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 the sauce from the heat and place the bowl on a kitchen towel. Whisk in the juice of 1/2 lemon until combined. Add salt to taste. Set aside.
Carefully take the skillet out of the oven and toss in 1/2 pound asparagus along with 1 tablespoons unsalted 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 3 ounces crab meat over the steak. Whisk the sauce and then spoon a generous amount over the crab and steak. Garnish with chopped flat-leaf parsley if desired. Serve extra sauce on the side.