I recommend prepping all ingredients before getting started to make it easier. The meatballs and sauce both use minced garlic, so be sure to mince it all at once (I use a garlic press to make this go fast). Add the canned tomatoes (with juices) to a large bowl and use your hands to break the whole tomatoes up.
To start the sauce, add the olive oil, butter, and onion to a soup pot or Dutch oven and sauté over medium heat for 5 minutes.
Stir in the garlic and cook for 30 seconds.
Add in the tomatoes, Italian seasoning, oregano, sugar, and red pepper flakes. Give it a good stir. Once the sauce starts to bubble, cover the pot with the lid slightly open and reduce the heat and simmer for 30 minutes (adjust between medium-low and low heat as needed to maintain a constant simmer).
While the sauce is cooking, make the meatballs. Add the breadcrumbs and milk to a fairly large prep bowl. Mix/mash together until you've got a paste.
Add the remaining meatball ingredients to the bowl. Using your hands, mix it together and then form about 18 (1 ½-inch) meatballs. Don't over-mix or pack them too tightly, and use a delicate touch. Place the meatballs on a couple of plates or a parchment paper lined baking sheet as you go along for easy clean-up.
Give the sauce a stir, then place the meatballs in the pot and gently arrange them so they're submerged in the sauce. Continue simmering (lid slightly open) for another 35-45 minutes or until they're cooked through (165F). You may need to increase the heat to get it going again, then reduce the heat and adjust as needed to maintain a simmer.
Give the sauce a taste and season with salt & pepper as needed (I'm generous with both). Serve with cooked spaghetti, more freshly grated parmesan cheese, and some fresh basil if desired.