Scorch leek until the outside skin blackens, either over a gas stove or in a 250°C oven.
While the leek is still hot, remove the blackened outside layers and set aside.
Once cool, roughly chop.
Fill a pot with salted water and bring to the boil.
Cook the casarecce in the salted water.
In a pan, brown off the butter with the crushed hazelnuts and capers.
When the butter has coloured, add the chopped leeks and a ladle of pasta water.
Add radicchio.
Just before the pasta has reached al dente, add to the sauce and finish cooking.
Add more pasta water to maintain a wet consistency.
When the pasta is cooked, add the squacquerone, a squeeze of lemon, and salt and pepper to taste.
Toss lightly and garnish with parsley and roasted hazelnuts to serve.
