In a large frying pan over medium-high heat, cook the onions with the butter until the onions are translucent. Add the bacon and the wine. Lower the heat and let it cook for a couple of minutes. In a large serving bowl, beat the 2 eggs with salt (not too much) and the pepper. Add the Parmigiano and incorporate well.
Meanwhile in a large pan, boil the water with salt. Cook the pasta al dente and drain. Immediately pour over the egg mixture and mix well. Add the bacon-onion-wine sauce and mix well. Serve hot.