Preheat oven to 400 degrees.
Toss cherry tomatoes lightly with olive oil. Spread out in an even layer on a sheet pan or baking dish. Roast for 25 to 30 minutes until the tomatoes have burst and are just beginning to shrivel.
Meanwhile, add 1/4 cup olive oil to large saucepan and heat over medium heat. Add onions and cook until softened. Add garlic and cook another few minutes until golden. Add the tomatoes, including all of the cooking liquid, and herbs and stir to combine. Season with salt and pepper to taste.
Turn the heat down to low, partially cover the pot with the lid and let simmer for at least 25 minutes, up to an hour, stirring infrequently.
Cool slightly. Transfer sauce to a blender and blend until sauce reaches the desired consistency. Taste again and season with salt and pepper as necessary.