450g white fish, 2 egg whites, 1 tsp salt, 1 tsp sugar, 4.5 tbps cornflour, 4.5 tbsp sake, 1 tbps mirin, food colouring if you desire.
Chuck everything in a blender and shape the resulting paste into whatever you like. If you want, colour it, roll it, have fun. Whatever you do, wrap it up in a foil sausage so it can be steamed.
Steam for 20 minutes, then chill. Ready for use. Easy as.