In a food processor, whizz the shallots, chillies, garlic, ginger, lemongrass, garam masala and 2 tablespoons water.
Heat the oil in a pan and gently cook the paste, for 2-3 minutes, until fragrant. Pour in the coconut milk and 100ml water, and add the tamarind paste, then simmer gently for 15 minutes, adding in the green beans and pepper for the last 10 minutes. Stir through the steak for the last 2-3 minutes of cooking time (for rare).
Meanwhile, put the rice in a pan with 500ml cold water. Bring to the boil, then turn down and simmer for 12 minutes, covered.
Stir the fish sauce, lime juice and ¾ of the coriander through the curry and serve with the rice and garnish with the desiccated coconut and remaining coriander leaves.
Cook's tip: this recipe also works really well with chicken, instead of beef. Just add in diced chicken breast or thighs at the same time as you add the green beans and peppers, cooking for 10 minutes until the chicken is cooked through. For a lower-fat option, use light coconut milk.