How to Make It
In a large bowl, soak the bread in the milk for 1 minute, mashing it. Using your hand, press out the milk and drain it off. Add 1/3 cup of the pesto, the scallion and the egg to the soaked bread and mash to a paste. Add the ground turkey and beef and season with 1 1/2 teaspoons of kosher salt and 1/2 teaspoon of pepper. Mix until well blended.
Line a baking sheet with plastic wrap. Using lightly moistened hands, roll the meat mixture into twenty-four 1 1/2-inch balls and transfer to the baking sheet.
In a large skillet, heat the olive oil until shimmering. Add the meatballs in a single layer and cook over moderately high heat, turning occasionally, until browned all over and cooked through, about 10 minutes.
Meanwhile, in a saucepan of boiling salted water, cook the fettuccine until al dente. Drain the pasta, reserving 1/4 cup of the cooking water. Transfer the fettuccine to a large bowl. Add the remaining 2/3 cup of pesto and a few tablespoons of the reserved pasta cooking water and toss until the pasta is evenly coated and moistened. Transfer the pasta to a large platter, leaving some of the pesto in the bowl. Add the meatballs to the bowl and toss with any remaining pesto. Scatter the meatballs on the fettuccine, sprinkle with Parmesan cheese and serve.
More Saucy Ideas: Stir the pesto into mixed ground meats to make meat loaf, serve it on bruschetta with shaved Parmesan cheese, stir it into soups or whisk it into vinaigrettes.