Move the steak from the freezer to the fridge on the morning of the day you’d like to cook it. Remove it from the fridge about an hour before you want to eat. Steak will cook more evenly when it is at room temperature. Whip up the salsa. Wash and finely chop the spring onions and the chard stems. Toss with the chopped lovage, the juice from half a lime and salt and pepper. Season the steak generously on both sides with salt and pepper. Heat a heavy cast iron pan over medium-high heat. The vegetable oil (we’re fond of grapeseed) will help the heat transfer from pan to steak. Sear the steak on each side for about three to five minutes. Remove from the pan and let rest for five minutes. Wipe the pan clean and warm the tortillas. Slice the steak thinly and divide among the tortillas. Top with a bit of salsa, sour cream and a squeeze of lime.