Peel and finely slice the onion and garlic, then place in a large non-stick frying pan on a medium heat with one tablespoon of oil, the vinegar and a pinch of sea salt. Seed and finely slice the peppers, then add to the pan and cook with the lid on for ten minutes, or until softened but not colored, stirring occasionally. Meanwhile, bash the pistachios in a pestle and mortar until fine.
Cook the pasta in a large pan of boiling salted water according to the package instructions, then drain, reserving a cupful of starchy cooking water. Finely grate the Parmesan into a blender, add the pepper mixture and a splash of boiling water, then whiz until smooth and season with salt and black pepper. Toss the pasta and sauce together, loosening with a splash of reserved cooking water, if needed. Finish with a dusting of pistachios and a fine grating of Parmesan.
Always good with a fresh crunchy herby green salad.