Finely dice the onion and garlic. Cook in a large pot with 3 Tbsp of olive oil until very soft and slightly golden brown. I wanted to make a sweeter sauce which is why I let the onions and garlic caramelize a bit. If you don’t like sweet sauces, proceed to the next step before they get any color on them.
Add the rest of the ingredients (crushed tomatoes, tomato paste, basil, oregano, bay leaves, brown sugar and balsamic vinegar) to the pot. Simmer on medium/low for one hour. Be careful of the splattering sauce! Leave a lid on the pot but slightly ajar to allow steam to escape but keep flying blobs of sauce from landing on your counter top.
Taste the sauce after a half hour or so and adjust spices and seasoning to your liking. The proportions listed above yield a slightly sweet and tangy sauce. If you like savory sauces, leave out the balsamic vinegar and reduce the sugar to 1 tsp. Some sugar is usually needed to balance the high acidity of the tomatoes.