You can always find a decent steak at Costco. Costco filet mignons are actually much better than "decent." In fact they are pretty darn good especially if they are cooked perfectly. The only trouble is that they are about 2 inches thick which means you need to spend some extra time considering your grilling methods. Let's take a look:
2 inch Costco filet mignon
Grillmates Montreal Seasoning
With steaks this big I like to cover them in Montreal steak seasoning and let them sit at room temperature for about 30 min. Not only does this let some of the salts from the seasoning penetrate into the meat a bit but it also means you will not be grilling cold steaks. This can be trouble for a 2 inch steak. Well, unless you like rare.
As for any steak I prepared a high heat on the grill. I filled my charcoal chimney up to the top and let the coals get nice and hot before dumping them out. When I dumped the coals out I placed them only on the right side of the grill. This gives me direct and indirect areas to cook on. The plan of attack is 3-4 minutes per side over direct heat followed by about 5 min per side of indirect heat. The idea is that you will sear the steak first and then finish the cooking over indirect heat.
The above picture shows the steaks after their first flip over direct heat.
After the direct heat grilling I moved the steaks over to the indirect side. At this stage they were very tender to the touch, meaning they were barely even rare inside. Moooooooo. Not quite yet.
After the 2nd flip over indirect heat the steaks were a bit more firm to the touch meaning that they were probably in the medium stage of doneness. Just right. At this time I took them inside and put some butter on top.
Wow, look how that butter melts on top of those filets!!
Now here I go again. I forgot to take a picture of me cutting into the steak. I guess that's the problem with the photographic subject being so delicious. I couldn't help myself. Here's what happened: The men of the group were perfectly happy with their medium/medium rare steaks and sadly the ladies of the group requested that their steaks be placed back on the grill for a bit longer. Hey, no problem by me. Remember: It is always better to undercook your steak and have to toss it back on. You NEVER want to serve someone a steak that is well done if you were aiming for medium.
I learned something while writing this up. Mignon is French for "dainty, cute, and small." So the French are responsible for naming this cut of meat. As you may know the Filet Mignon comes from the tenderloin. The tenderloin is a non weight bearing muscle which is why the steak is so tender. Just thought I'd share.