This recipe has several components, and timing is important. I suggest making the butter and vinaigrette ahead, leaving you time to focus on the steak and fries as they cook fairly quickly, and take about the same amount of time all in.
Take the steak out of the fridge at least 30 minutes before cooking, to allow it to come to room temperature. Pat the steaks dry, coat lightly in olive oil, and season LIBERALLY with kosher salt and pepper. You want to really see the salt and pepper on both sides of the steaks.
Preheat the oven to 425 degrees, or whatever your frozen fries packaging suggests. Preheat your grill, or grill pan to medium high heat.
Bake the fries according to package instructions, making sure not to overcook. Usually about 18 -20 minutes total - I also use two 1/2 sheet pans to make sure they don't steam with over crowding.
Sear the steaks about 4 minutes a side, or more depending on your preference for doneness - we prefer medium rare, which is quick with a thin cut like skirt steak. The steak will continue to cook after you take it off the grill. When it's done, set it on a patter, top with slices of the chive butter, and let it rest for about 10 minutes to allow the juices to settle back into the meat.
When ready to serve, toss the fries with salt, pepper, truffle oil and a tablespoon or two of chopped chives. Slice the steak against the grain, as desired, and top with extra salt and pepper. Dress the watercress with some of the vinaigrette (you will have extra, which will keep for a week or two in the fridge), and throw all this deliciousness on a plate together to eat immediately!