Mash the butter with the spring onions ginger and soy, gradually working in the soy. You can leave it at room temperature or put it in the fridge to chill. Some people like to chill it a little, then shape it into a log and wrap it in baking parchment. You can then cut the butter into rounds.
Heat oven to 140C/120C fan/gas 2 and put an empty roasting tin or a metal baking sheet large enough to hold all the steaks into it.
Heat a large frying pan (or 2 smaller ones) – use a cast iron one if you can – for 7-10 mins before you want to start cooking. Add a tiny bit of flavourless oil. When the pan smokes, it’s ready for the steaks.
Add the steaks to the pan. Quickly hold the fat on each of them against the base of the pan to render a little fat and colour it, then lay the steaks flat and press down with your tongs. Season with salt and flip the steaks over frequently, moving them round the pan and making sure you can hear them sizzle. If the pan gets too hot, and the surface is getting too dark, turn the heat down (you want a good dark colour, but you don’t want to burn it). Once the surface is well coloured – this should take about 4 mins – transfer the steaks to the hot sheet or tin in the oven. Finish cooking the steaks in the oven – 2 mins for rare steak, 5 minutes for medium-rare. Serve with a knob of the soy butter melting over the top, some Asian greens and chips.