Clean and finely chop the onion. In a large saucepan, heat 2 tablespoons of olive oil over low heat and add the chopped onion. Sauté until soft.
While the onion cooks, clean and chop the carrot and celery. Once the onion is softened, add the carrot and celery to the pan and sauté together.
Add the ground beef and pork to the saucepan, breaking it apart with a wooden spoon. Cook until the meat is well browned.
Pour in the glass of red wine and let it simmer until the alcohol has evaporated.
Add the peas, tomato puree, and 2-3 ladles of hot water to the mixture. Season with salt, cover with a lid, and let it simmer on low heat for about 1.5 hours. If the ragù becomes too thick, add another ladle of hot water.
Once cooked, you can stir in a couple of tablespoons of whole milk for added creaminess. This tip comes from my experience with authentic Bolognese ragù!
Adjust the salt and add freshly ground black pepper to taste.
In a separate pot, cook the tagliatelle according to package instructions. When there are 2 minutes left, transfer the pasta to the saucepan with the ragù, tossing to combine until fully cooked.
Remove the pasta from heat and mix in a couple of tablespoons of grated Parmigiano Reggiano.