Pour the stock into a large saucepan and add the garlic cloves, lemongrass, ginger, cloves, cinnamon and chillies. Bring to the boil and simmer for 15 minutes. Remove from the heat and let the stock sit for 15 minutes to allow the flavours to infuse.
Meanwhile, heat a large frying pan or griddle. Rub the steak with vegetable oil and when the griddle or pan is hot, cook the steak for 2 minutes on each side. Remove and allow to rest for 2 minutes then slice.
Bring a pan of water to the boil and cook the rice noodles for 4-5 minutes or until just tender. Drain and set aside.
Pour the stock through a sieve and return to the hob. Bring to a simmer and add the fish sauce, spring onions and coriander, mint leaves.
Divide the noodles and the beef slices between two large bowls. Pour over the soup and garnish with the bean sprouts, herbs, spring onion, wedges of lime and kimchi sauce.
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