Cook leek | Meanwhile, heat the butter and olive oil in a large frying pan over a medium heat
Add the leek, garlic, chilli flakes and a pinch of salt, then cook with the lid on, but stirring occasionally for 12-15 minutes until soft and beginning to take on a little colour
Combine | Stir in the miso paste and pasta and toast for a minute or two
Add in the vegetable stock and bring to a simmer | Cook with the lid off until the pasta is al dente until al dente, adding a little more water i fit reduces too quickly
Stir in the lemon juice | Taste and season with salt, pepper or more lemon
Serve | Divide the pasta between bowls and sprinkle over the lemon zest and more chilli flakes | Serve