Heat the olive oil in a frying pan over a high heat. Once nearly smoking, add the duck breast, skin side down, and cook until the skin is a lovely deep golden brown colour. Do not flip over. Remove from the pan and cut into slices 2cm thick. Toss the duck slices in the red curry paste and allow to marinate for at least 30 minutes.
In the same frying pan over a medium heat, cook the onion until soft. Add the minced garlic, lemongrass, chilli, spices and sugar and cook and stir for 2 minutes. Add the chicken stock and lime juice and bring to the boil. Season. Immediately lower the heat and add the sliced duck, simmer gently for 30 minutes until the duck is tender.
Just before cooking time is up, add the coconut milk and chopped fresh coriander and heat through. Serve with a dollop of crème fraîche.