Heat a large, wide pan on medium-high heat. Add the olive oil and leek or onion and cook for 3-4 minutes until tender. Add the orzo (risoni) and stir to coat. Pour in the stock, stir and cover with lid. Cook for 6 minutes, reducing the heat to medium if it bubbles too aggressively, and then check the orzo - it should be slightly soft but not quite done, with still be quite a lot of liquid in the pan. Add the asparagus and drizzle it with olive oil, and a pinch of salt, cover again and cook for 2 minutes, until the asparagus is crisp tender and bright green and the pasta is fully cooked and al dente.

Uncover and add the zest and juice of the lemon, butter, miso paste, dill and stir to melt the butter and miso through the pasta. Taste and season well with sea salt and black pepper, adding more lemon juice if you like. Serve immediately.