Make the chicken meatball mixture: Place the chicken mince, curry paste, makrut lime leaves and salt in a bowl. Mix until well combined. Set aside while you start your broth.
Make the curry broth: Heat the vegetable oil in a large pot over medium heat. Add the red curry paste and cook, stirring, for about a minute until fragrant. Pour in the coconut milk. Crush the makrut lime leaves in the palm of your hand to release their flavour. Add the chicken stock cubes and 4 cups of water. Stir through the fish sauce and sugar. Bring to a gentle simmer, then turn the heat to medium-low.
Cook the meatballs: Slightly dampen your hands with water (this makes the mixture less sticky) and pinch off roughly 1-2 teaspoonfuls of the mince. Drop the rough little meatballs straight into the gently simmering curry broth. Repeat until all the mixture has been used up. Simmer for a further 4-5 minutes or until the meatballs are cooked through.
Cook the noodles and greens: Bring another pot of water to the boil. Cook the udon noodles until just tender (check packet directions). In the final minute, add the broccolini and blanch until bright green. Drain well.
Put it all together: Divide the noodles and broccolini among serving bowls. Ladle over the hot curry soup and meatballs. Top with coriander and crispy chilli oil, if using. Enjoy!
