Chop the crabmeat and place in a bowl. Add the mayonnaise and chives, and mix to combine. Season with salt, pepper and the lemon juice. Cover the bowl with plastic wrap and refrigerate until ready to use.
Make a shallow cut lengthwise into the beef and then continue cutting along the curve, until the beef is a flat sheet. Sprinkle the beef with salt and pepper. Spread the crab mixture in an even layer on the beef, then place the asparagus lengthwise over the crab with the tips poking out. Roll up the beef to make a pinwheel, then use butchers twine to tie it together in 1-inch increments. Heat an ovenproof saute pan over high heat and add some oil. Sear the beef on all sides, then transfer the pan to the oven and cook until the internal temperature hits 130 degrees F, 30 minutes. Remove the meat from the pan and rest on a cutting board before slicing.
For the potatoes: Place the potatoes in a saucepan filled with cool salted water. Cook the potatoes until tender, then drain and cool. Using your thumb or a spoon, smash the potatoes until they break apart slightly. In a straight-sided saute pan add enough oil to come 1-inch up the sides of the pan. Heat over medium heat until a deep-frying thermometer reads 365 degrees F. Add the rosemary and fry until crispy, then remove with a slotted spoon and drain on paper towels. Fry the potatoes until golden brown and crispy, then remove with a slotted spoon and drain on paper towels. Season with the flaky sea salt and pepper, and garnish with the fried rosemary.
For the bearnaise: In a small saucepan set over medium-high heat, combine the vinegar, wine, shallots, bay leaf and half of the tarragon. Bring to a simmer and cook until reduced by half. Remove from the heat and set aside to cool. Pour through a fine mesh sieve to strain out the solids.
In the pitcher of a blender, add the yolks and the vinegar reduction. With the blender running, add one-third of the butter in a slow, steady stream. Once it emulsifies, increase the blender speed to high and add the remaining butter. Add the remaining tarragon leaves, then season with salt and pepper and give it one more buzz. Set aside in a warm spot to hold the sauce.
Slice the beef into two portions and serve with the potatoes and bearnaise sauce.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.