2–4 tablespoons of vegetable oil for sautéing the meatballs (I use olive oil or canola)
In a large bowl, combine ground turkey, onion, garlic, egg, tomato paste, sweet potato, salt and pepper. Stir with a fork until everything is well mixed. Sprinkle in flour and stir until just combined. Cover the bowl with plastic wrap and chill in the fridge for at least 1/2 hour or up to 4 hours. You can omit this step, but the mixture will be mushy and harder to shape into balls. The longer you chill the mixture, the easier it will be to roll the meatballs.
Set a large plate on your work surface. Roll all the meat into balls – a heaping tablespoon at a time. Set the meatballs on the plate as you go. If your hands are getting sticky, fill a small bowl with ice water and dip your hands in periodically. If your hands are cold and wet, the meat is less likely to stick to them.
Once all the meatballs are rolled, heat 2 tablespoons of oil over medium heat, in a large heavy skillet, preferably cast iron or non-stick. Once the oil is nice and hot, add half the meatballs. Sauté the meatballs for 5 minutes or so, turning them gently with a spatula every minute or so, to brown them on all sides. Transfer the browned meatballs to another plate. Cook the rest of the meatballs, adding more oil if the pan is dry.
Return all the meatballs to the skillet and add 4 cups of your favorite marinara sauce and 1/2 cup of water. Simmer the meatballs in the sauce for 25 minutes, until they’re cooked through.