How to Make It
In a pot, heat the oil. Add the carrot, onion and celery, season with salt and pepper and cook over moderately low heat, stirring, until the vegetables are very tender and caramelized, 20 minutes. Add the anchovies and tomato paste and cook, stirring, until the anchovies dissolve and the tomato paste is deep red, 5 minutes. Add the beet greens, season with salt and pepper, and cook, tossing occasionally, until wilted, 7 minutes.
In a bowl, soak the bread in the milk until the milk is absorbed, about 5 minutes.
In a large bowl, combine the beef, ricotta, Parmigiano, egg, lemon zest, crushed red pepper, parsley, fennel, kosher salt and black pepper. Squeeze any excess milk from the bread and add the bread to the bowl. Mix the meat mixture well, then roll it into eighteen 1 1/2-inch balls; transfer to a baking sheet.
In a cast-iron skillet, heat 2 tablespoons of the canola oil. Cook half of the meatballs over moderate heat, turning, until golden brown and no longer pink within, about 15 minutes. Repeat with the remaining 2 tablespoons of canola oil and meatballs.
Rewarm the beet greens and transfer to a platter; top with the meatballs. Serve garnished with Parmigiano, chopped oregano and sea salt.