Mandy Yin's Sarawak white chicken

Name: Mandy Yin's Sarawak white chicken
Cuisine: Asian
Ingredients: D; For prepping the chicken; 6 skinless, bone-in chicken thighs; 1 tsp salt; For the spice paste; 200g (7oz) onion, roughly chopped; 2 garlic cloves; 2½cm (1in) piece of ginger; 2 lemongrass stalks, roughly chopped; For cooking the chicken; 1 tsp black peppercorns, preferably Sarawak; 1 tsp white peppercorns, preferably Sarawak; 3 tbsp vegetable oil; 450g (1lb) tomatoes, cut into eighths; 300ml (10½oz) water; 5 laksa leaf stalks with leaves still attached (see Note); 100ml (scant ½ cup) coconut milk; For the garnish; ½ handful picked laksa leaves or mint leaves; ½ handful freshly picked coriander leaves; 1 red onion, quartered then finely sliced into semicircles; 2 red chillies, finely sliced; juice from ½ lime