Lay the tomatoes, onions, and garlic out on a baking tray, drizzle with the olive oil, and sprinkle with salt and pepper.
Place the tray into the oven and roast for 20 minutes or until everything is soft and a little browned.
Put the roasted vegetables in the blender and add the herbs. Blend until it reaches the desired consistency.
Notes
Give the tomatoes and onions time to roast. If you rush them by turning up the heat, you'll end up with subpar product.
For Italian herbs, turn to basil and oregano. Fresh are best, but dried herbs will do the trick in a pinch. Just remember dried herbs are usually more potent so adjust the amount as necessary.
Garlic is integral to this recipe. Without it, you won't achieve that deep, robust flavor you're after. In fact, add an extra clove or two, if you really like the stuff.