For the blue cheese butter: Whisk together the butter, blue cheese, chives, honey, mustard and lemon zest in a bowl until uniform. Season to taste with salt and pepper. Using a spatula, scrape out onto plastic wrap, then form into a log and refrigerate until firm, about 1 hour.
For the black powder rub: Toast the sesame seeds, peppercorns, poppy seeds and mustard seeds in a dry pan until fragrant, 1 to 2 minutes. Transfer to a small food processor, blender or spice grinder along with the salt, brown sugar, granulated garlic and dehydrated onion and pulse until finely ground.
For the rib eyes: Preheat the oven to 225 degrees F. Line a sheet pan with foil and fit a rack inside.
Brush the steaks with vegetable oil and coat in a good amount of the black powder rub. Place on the wire-racked sheet pan and roast until the internal temperature registers 115 to 120 degrees F, 1 to 1 1/2 hours.
Heat a large cast-iron skillet over medium-high heat. Add a little vegetable oil to the bottom and sear the steak until properly charred, about a minute per side. (Don't forget to hold the steak upright with tongs to sear the edges.) Transfer to a warm plate. (See Cook's Note.)
Slice a medallion of the cold blue cheese butter and place it on top of each steak. Very carefully ignite a rosemary sprig with a torch to get it smoking (blow out any flame; you just want the smoke) and place it on top of the steak and butter. Immediately cover with a cloche or dome to trap in the smoke. Repeat with the remaining steak. Serve and slice tableside, if desired, into manageable pieces.
Roasting the steak first, then searing it, is called a reverse-sear, and it yields excellent results on a thick piece of beef.
Propane gas torches are highly flammable and should be kept away from heat, open flame and prolonged exposure to sunlight. They should be used only in well-ventilated areas. Follow torch manufacturer's instructions for use.