Yellow pumpkin & potato curry

Ingredients

• 2 tablespoons oil
• 1 red chilli, seeds removed and finely chopped
• 1 red onion, finely chopped
• 2 centimetre piece of ginger, grated
• 2 cloves garlic, crushed and chopped
• 1 teaspoon ground coriander
• 1 teaspoon ground turmeric
• 1 teaspoon ground cumin
• 3 tablespoons fish sauce
• 1 tablespoon brown sugar
• 2 teaspoons prepared lemongrass
• 2 x 400ml cans coconut milk
• 1 tablespoon lemon juice
• 1 tablespoon tomato paste
• 750 grams pumpkin, peeled and chopped
• 3 1/2 potatoes (750g), peeled and roughly chopped
• coriander leaves for garnish