Preheat the oven to 180℃/350F, fan 200℃/400F or Gas Mark 6.
Melt HALF of the butter in a large saucepan and add the leeks. Cook over a medium heat for 3-4 minutes until starting to soften.
Meanwhile, put the smoked haddock into the oven on a baking tray and cook for 20 minutes until cooked through.
Add the rice to the saucepan and cook, stirring for 1-2 minutes.
Gradually add the stock a ladle at a time, stirring all the time. Try to add the next ladle when the one before has been absorbed.
Do the same with the milk when the stock is all gone. This whole process will take 15-20 minutes. The rice should still have some 'bite' and texture to not be overcooked.
Remove the fish from the oven when the cooking time is up.
Take the risotto off the heat, add plenty of salt and pepper, the peas and the remaining butter. Break up the fish and stir through too (the heat in the risotto will just warm the peas through).
Stir through the cheese and top with fresh chives to serve.