Make the miso base: Place the miso paste, peanut butter and sesame oil in a small saucepan. Add half the chicken stock and whisk until smooth and well combined. Then mix in the remaining chicken stock. Place over high heat, cover and bring to a simmer.
Add the noodles: Remove the lid and drop the udon noodles into the broth. Cook for about 2 minutes, using chopsticks or tongs to help loosen them up.
Poach the egg: Turn the heat down to low so the broth is just gently simmering. Crack the egg into a small bowl, then carefully pour it into the broth. Let it poach gently for 2-3 minutes until the white is set and the yolk is still soft (or cook it to your liking).
Add the greens: Carefully place the baby spinach into the broth, doing your best not to disturb the egg. Cook for another 30 seconds, just until wilted.
Serve it up: Use tongs and a ladle to transfer everything into a bowl (I like to use a slotted spoon to handle the poached egg). Top with sliced spring onion, a sprinkle of sesame seeds and a drizzle of chilli oil. Eat immediately while the egg is jammy and the noodles are still beautifully slurpy.
