Onion, preferably red.
My standard super-cheap pasta sauce recipe is:
- chop onion(s), garlic
- heat olive oil in a pan
- gently sautee onions until translucent, add garlic, sautee a bit more
- dump a can of tomatoes (or fresh, peeled tomatoes, but you get good quality cans nowadays)
- add dried (or fresh) tyme, herbes de provence, whatever seasoning you like, salt, black pepper (plus crushed chili)
- let simmer until great, the longer the better -- it's kinda edible after 20min, but if you can let it simmer for 45, it's better.
If you add ground beef, carrots, other vegetables it might be necessary to let simmer for 1.5h. Some vegetables need to be added late (peas...).