This is one of my favourite noodle dishes. Marinating the beef makes it very tender. I use light soy sauce but the original recipe calls for dark soy which is slightly sweeter. You can use either or a combination of both. The rice noodles have a tendency to stick together but I find microwaving them for a minute or so and then separating them seems to do the trick. Also the wok needs to be really not when cooking them. I don't deseed the chillies but you may prefer to.