Heat the oil in a saucepan and cook the onion and garlic until onion is softening, about 5 minutes. Add the capsicums and cook another 5 minutes.
Place the onions and capsicums in a food processor or blender and add the milk, sour cream and cream cheese. Puree until smooth. Season with salt and pepper to taste.
Cook the farfalle in boiling salted water until al dente. Drain and return to the saucepan and then add the pureed sauce and smoked salmon. Stir in the butter. Serve hot.