In a large bowl, stir together the spinach, ½ cup of the spinach liquid, panko, egg, 1 teaspoon chopped garlic, 1 teaspoon Diamond Crystal kosher salt (or ½ teaspoon coarse kosher salt) and a few grinds of pepper. Let sit for 5 minutes, until the panko is softened.

Add the beef, pork, Parmesan and parsley. Mix with your hands until just combined, avoiding overmixing. Using oiled hands, roll the mixture into 18 balls (each about 2 heaping tablespoons, about 50 grams each) and place on a plate or sheet pan as you go. If the meat is soft and not holding its shape, refrigerate for 5 to 10 minutes to firm.

In a large Dutch oven or heavy-bottomed pot, heat the oil over medium. Working in batches to avoid crowding, add the meatballs and cook until browned on two sides, 3 to 6 minutes per side. Return to the plate and repeat with the remaining meatballs. (They will not be cooked through yet.)

Without cleaning the pot, reduce heat to medium-low and add the remaining garlic. Stir to coat in the fat, then carefully add the crushed tomatoes, the herb sprigs and a pinch of salt. Scrape up the stuck-on browned bits. Once gently simmering, add the meatballs and any drippings from the plate. Cook, flipping the meatballs occasionally, until the meatballs are cooked through and the sauce is rich, 20 to 25 minutes. Turn off the heat.

While the meatballs are simmering, bring a large pot of salted water to a boil. When the meatballs are done, add the pasta to the water and cook until al dente according to package directions. Reserve 1 ½ cups pasta water, then drain and return the pasta to the pot.

Add about 1 cup of the tomato sauce to the pasta, along with ½ cup pasta water. Toss over medium-high until the pasta is glossed in sauce; add more sauce and pasta water as needed until lightly coated. Serve the pasta topped with the meatballs, more sauce and more grated Parmesan.