To make the mayo: In a small bowl, mix the wasabi powder with 1 teaspoon water to make a paste. Mix the wasabi paste, remaining water and mayonnaise together. Season with some sugar, and set aside.
To make the spicy coating: Mix all the ground cumin, dried chile flakes, black pepper, and salt, on a plate.
To make the beef: Prepare the fillet by hammering it with a meat mallet, or the side of a Chinese cleaver. Slice the beef into wafer-thin slices, and coat the pieces in the spice mix.
Heat a wok or pan over high heat and add the groundnut oil. Add the beef and stir-fry for less than 1 minute until browned and tender. As the beef starts to cook, pour in the rice wine or sherry, and season with the soy sauce, and a pinch of salt. Remove the wok from the heat and stir in the cilantro, and spring onions. Serve immediately. You can serve the spiced beef in steamed thin wheat flour pancakes, stuffed into warmed flatbreads or rolled in warmed tortilla wraps topped with plenty of wasabi mayo.
You will not need the water if using creamed horseradish.* *Wasabi is a Japanese variety of green horseradish, more fiery than white horseradish. It always accompanies sushi. If you find wasabi powder, just combine the powder and warm water to make a paste, or add warm cream. This is not a Chinese recipe but it's fantastic!