Place all the paste ingredients into a blender and blitz until it forms a paste.
Place the noodles in a heatproof medium bowl, cover with boiling water and leave to soak for 5 minutes until tender. Drain and cool.
Heat the oil in a wok over a high heat. Add the steak and paste and stir-fry for 2-3 minutes until fragrant and the meat is slightly charred on the edges. Add some more coconut milk if the mixture becomes too dry.
Add the fish sauce. Toss in the spring onions, noodles, coriander and basil and remove from the heat.
Turn out into a bowl and squeeze over some lime juice. Sprinkle a couple of leaves of coriander and basil on top to serve.