Massaman curry roast chicken

INGREDIENTS

• whole chicken , about 1.8kg
• two thumb-size pieces root ginger
• 1 stick lemongrass , bashed with a rolling pin
• 1 lime , cut into quarters
• 70g/2.5oz pack Massaman curry paste (I used Blue Elephant)
• 1 tsp olive oil
• 450g baby new potatoes , any larger ones halved
• 400ml/14fl oz can coconut milk
• 1 tsp brown sugar , any type
• 200g green beans , trimmed
• 1 tsp fish sauce
• 2 tbsp unsalted peanuts , crushed (optional)
• basmati rice , to serve