Pile the flour up on your work surface and make a “well” in the centre; break the eggs into it, add the salt and the olive oil. Start mixing the eggs and flour with a fork, then use your fingertips and, finally, with your hands. Continue to knead vigorously and with regular movements for about 15 minutes. When the dough is smooth and elastic, shape it into a ball, wrap it in clingfilm and put it in the fridge for an hour. In the meanwhile wash and clean the vegetables, then cut them into broad, thin slices (only use one of the onions). Grill them until “al dente” (= firm to the bite) in a grill pan and then coarsely chop them with a mezzaluna knife. Put a heavy-bottomed frying pan on the stove with the oil and the other onion, finely chopped. Sauté it and then add the vegetables, season with salt and cook for 5 minutes stirring frequently. Take the pasta dough out of the fridge, roll it out as thin as you can and cut it into strips 10 cm wide and 20 cm long. Arrange the vegetables on top of each strip forming a row lengthwise, take one edge and fold the pasta over on top of the vegetables making the edges meet, and close, sealing the three sides together with a pasta wheel; you will obtain a “parcel” roughly 5 cm wide and 20 cm long. Hold one end of the “parcel” with two fingers and use the other hand to wrap it around them, forming a “roll”. Lay it on your work surface and join the ends of the pasta together, both on the inside and on the outside, so that the “rolls” already prepared don’t open up when they’re cooked. Bring some water to a boil in a deep saucepan, add salt and delicately put the “rolls” into it (they cook in 5 minutes). In the meanwhile put a heavy-bottomed frying pan over a low heat with the butter and some salt and pepper. Strain the “rolls” and lay them in the frying pan upside-down (with the part with more pasta facing downwards because it’s the part that needs to cook longer). Add a ladleful of the water they were boiled in and continue cooking for another 5 minutes. Serve your beautiful pasta “rolls” nice and hot with grated Parmigiano (or smoked ricotta if you can fins some) and buon appetito!