We keep it pretty simple, just rub with a little salt and pepper on the beef fillet, let sit till room temperature (or close). Then put the fillet on a heated grill on medium-high for 3-5 minutes on each side to cook rare or medium rare.
Grass-fed beef can be a little tricky to cook because it tends to be tough. It is worth it, though, because the health benefits over grain-fed beef are significant. Grass-fed beef is leaner and offers 2-4 times more omega-3 fatty acids (“good fats”). It also is richer in antioxidants including vitamin E, C and beta-carotene. Not to mention that they are usually free of added hormones and antibiotics.
The two ways to go are cook it long and low or quick and rare.