Bring salted water in a 8-quart or larger stockpot to a boil and cook fettuccine according to package directions. When pasta is done, drain, reserving 1 cup cooking liquid.

While the pasta is cooking, begin making the sauce: In a 12-inch or larger sauté pan, heat olive oil over medium-high heat. Add onion, shallot, 1/2 teaspoon salt, and 1/4 teaspoon pepper and cook until onions are translucent, about 2 minutes. Add garlic, bacon and peas and cook 2 minutes longer. Add reserved pasta, parsley, cheese, and extra virgin olive oil and cook, tossing, until heated through and well combined. (If necessary, add a bit of reserved pasta-cooking water a little at a time to moisten.)

Remove pasta from heat and transfer to a large serving bowl or to individual serving bowls. Sprinkle with additional cheese and black pepper if desired. Top with chives and serve immediately.