Preheat oven to 325°F with one rack on the middle setting and another in the lowest setting (for the meatballs).
Heat large oven safe pot or Dutch oven over medium-low heat. Add 1 tablespoon olive oil and swirl it around. When it starts to shimmer, add the minced onions and sauté until translucent, stirring occasionally.
Add the minced garlic and cook, stirring frequently, for 1 minute. Then add the 2 cans of crushed tomatoes and stir to combine.
One at a time, add the whole peeled tomatoes, squeezing each tomato in your hand over the pot before gently dropping it in. Once all the tomatoes are in, pour the remaining liquid from the can into the pot and stir.
Add the carrot, onion quarters, bay leaves, basil stems, red pepper flakes, dried oregano, pinch of salt, and a few grinds of pepper to the pot. Stir until everything is submerged.NOTE: Don’t add too much salt in this step. Just a pinch will do. It’s about to reduce, and if it’s too salty now it’ll be wayyyy too salty later. Put the lid on the pot at a slight angle so that steam can escape, and place it in the oven for 2-3 hours until it has reduced by ⅓ and is deep red in color. Stir every hour.NOTE: If making meatballs, now is a good time to do so!
When the sauce has reduced and taken on a dark red color, take the pot out of the oven and use a slotted spoon or wire spider to remove and discard the carrot, onion halves, bay leaves, and basil stems. Stir in chopped basil and parsley. Add salt and pepper to taste.
If eating immediately, keep the pot on the stove on low-medium heat to poach the sausages and heat the meatballs).If prepping ahead, let the sauce cool to room temperature before transferring to an airtight container and placing in the fridge or freezer.