In the meantime, warm the olive oil in a saucepan. When the oil shimmers add the garlic, the chopped onion, celery and carrots and let it cook for 5 minutes until tender.
Add the canned tomatoes to the can, chop them with a wooden spoon and let them cook until they have melted into a sauce, 10 to 15 minutes.
To make the meatballs
Start by putting in a bowl the ground beef, pork, 2 tbsp parmesan, 1 tbsp chopped parsley, 1 egg, 3 tbsp breadcrumbs, 2 tbsp pine nuts, fennel, garlic, salt, crushed black pepper, chili flakes and nutmeg.
Mix all the ingredients well and start rolling the assembled ingredients into a 2.5 inches diameter balls. This should yield around 25 meatballs.
At this point take a baking dish, spread the tomato sauce on the bottom and place on top the meatballs. Gently coat them with the tomato sauce, making sure they have a thin layer of sauce.
Bake them at 360°F (180°C) for 30 minutes.
To make the polenta
As soon as you start baking the meatballs, bring 1 l of water to boil, adding 1 tbsp of salt.
Pour like rain all the polenta, stirring continuously to avoid any lump.
Continue to stir for 10-15 minutes, until the polenta is creamy and reaches the desired consistency.
Serve it immediately, and place the polpette al sugo on top! MANGIA!
Notes
You can use different varieties of meat - you can use only beef or mix it with veal or turkey. You can add cold cuts as well.
You can use different types of cheese, though I recommend a hard cheese. If you want to stay in the Italian territory, I recommend Pecorino or aged Asiago. If you want to explore other varieties, I recommend Manchego or Vintage Gouda.
In terms of spices, you can mix and match whatever you prefer. If you want a more spicy hint, jalapeno powder will work well instead of dried chili flakes. Instead of nutmeg, you can try allspice, cumin or coriander. For more suggestions read the post.
The meatballs can be frozen - they will stay good for 8 weeks. You should let them thaw and then heat them in a pan with a bit of oil. I do not recommend a microwave as it will dry them out.