Blend all the paste ingredients together. Heat a wok over a high heat, add the oil and stir fry the shallots with the shrimp paste for less than 1 minute.
Add the paste ingredients and stir fry for 1 minute. Add the steak and stir fry for 2 minutes until browned on all sides.
Stir in the coconut milk. For a thinner sauce you could also add a little chicken stock at this stage or for a creamier curry you could add some coconut cream.
Add the lemon grass, the brown sugar, ground coriander, and fish sauce.
Bring to the boil and sprinkle with a handful of chopped fresh coriander and Thai basil leaves. Bring a large pan of water to the boil and cook the rice noodles according to the packet instructions, drain and place in 2 serving bowls. Ladle the curry over the noodles and serve immediately.