in a medium bowl, mash together all the ingredients. You can leave it in the bowl, roll into a tube in some plastic wrap and slice as discs. Chill in the fridge until ready to use.
Heat a cast-iron skillet over medium-high heat until it is very hot, about 5-6 minutes. Pat the steak dry with some paper towels and then season both sides with salt and pepper. Place the steak in the hot pan and DON'T TOUCH IT for 5 minutes, flip it once and leave it alone for another 4-5 minutes for medium-rare. I don't recommend it but you can leave it a little longer if you want it more well done. transfer the steam to a cutting board and let it rest.
remove all but 1 tablespoon of grease out of the pan and return the pant o medium heat. Add the butter, let it melt then add the garlic. Let the garlic cook for 30 seconds, careful not to burn it. Add the asparagus and the chicken broth and cook, stirring once in awhile, until the broth evaporates into a glaze and the asparagus is al dente, 2-3 minutes. season with salt and pepper
slice the steak and arrange on plates or a platter, dollop as much as you would like of the miso butter on top. place the asparagus along side.