Step 1

Bring a large pot of heavily salted water to a boil over high. Meanwhile, pulse onion, carrot, and celery in a food processor until very finely chopped (but not pureed), about 5 pulses, scraping down sides of bowl as needed. Heat oil in a large Dutch oven over medium-high. Add chopped vegetable mixture. Cook, stirring occasionally, until softened, about 5 minutes. Add tomato paste and garlic. Cook, stirring constantly, until tomato paste starts to darken, about 2 minutes. Add meat substitute in chunks. Cook, undisturbed, until brown on bottom, about 2 minutes. Break up meat substitute using a wooden spoon. Cook, stirring occasionally, until browned, about 4 minutes. Add wine, salt, fennel, and pepper. Cook, stirring occasionally, until wine has reduced, about 1 minute. Add tomatoes and milk. Reduce heat to medium. Cook, stirring occasionally, until ragù is thickened and saucy, about 12 minutes.

Step 2

During final 10 minutes of ragù cook time, add spaghetti to boiling water. Cook until almost al dente, 9 to 11 minutes.

Step 3

Using tongs, transfer spaghetti to ragù in Dutch oven, reserving cooking water in pot. Add about ¾ cup reserved cooking water to spaghetti mixture. Cook over medium, stirring with tongs, until noodles are loosened and coated with sauce. Remove from heat. Add butter and ½ cup of the Parmesan; stir and fold together until butter has melted. Divide among 4 plates; sprinkle with parsley and remaining ¼ cup Parmesan.