For the beef tenderloin: Put a rack in the center of the oven and preheat to 150 degrees F, or lowest temperature setting. Season the steaks liberally all over with salt and pepper. Place on a rack over a roasting pan and cook until an instant-read thermometer reads 125 degrees F when inserted into the thickest part of a steak, about 90 minutes. Rest for 10 minutes.
Meanwhile, make the habanero butter: Whisk together the butter, habanero, lime zest and juice, shallot, roasted garlic, parsley, salt and pepper. Refrigerate, covered, to firm up slightly.
Set a large cast-iron skillet over high heat. Get it extremely hot, and then add the grapeseed oil. Add the rested steaks and cook for 1 minute to add color, turn and cook 1 minute on the second side. Add the butter; as soon it starts to melt spoon it over the meat, and then immediately remove the steaks from pan. Rest 8 minutes and serve with the habanero butter on top.
To make roasted garlic, cut the top off a head of garlic (the pointy end), drizzle with a little olive oil, wrap in foil and bake at 350 degree F. until very tender when pierced with a knife, about 20 minutes. Cool, squeeze the cloves out of the skins, and mash or mince.