Prepare caramelized onions and de-shell crab leg(s) and roughtly chop meat. Butterfly beef tenderloin, cutting directly to the middle the whole way down, but allowing at least 1 1/2 inches on the bottom (so it doesn't split).
Melt butter in medium bowl along with garlic powder. Toss roughly chopped crab in melted butter.
Spread butterflied beef, cut side up, flat on a surface. Line center with crab mixture and then caramelized onions. Pull flaps together (it looks like it won't fit, but it will!) and tie tightly with kitchen twine every 1 1/2 inches.
Rub beef tenderloin will olive oil, and then massage with fine sea salt and pepper. Allow to sit for 20 minutes.
Preheat oven to 400 degrees. Place in oven and roast to desired temperature, 30 to 35 minutes for medium-rare, 35-40 for medium. Times will vary depending on exact thickness of your tenderloin.
Transfer to a cutting board. Tent and let rest for 10 minutes before carving. Remove twine and slice thickly. Enjoy your Crab Stuffed Beef Tenderloin.
If you've tried this recipe, come back and let us know how it was!