Bring a large pot of water to a simmer. While pot comes to a simmer, make a small "X" shape into the bottom of each tomato.
Using a slotted spoon, carefully lower several tomatoes into the water and simmer for about 30 seconds to one minute, or until you see the skins begin to split or pull away from the tomato.
Using the slotted spoon, transfer the tomatoes to a large bowl of ice water. Repeat with remaining tomatoes, working in batches. The ice water stops the cooking process and quickly cools the tomatoes, making them easier to handle.
Once cool enough to handle, remove the tomatoes from the ice water. Using a pairing knife, remove the stem and core from each tomato, while peeling away the skins (they should lift off easily).
Cut the peeled and cored tomatoes into quarters and add to the slow cooker bae.
Add chopped onion, garlic, Italian seasoning, tomato paste, sugar, salt, and pepper. Stir everything together.
Cover and set it to LOW for 6-8 hours. Or High for 3-4 hours. The tomatoes will release liquid as they cook.
At the end of cooking, add the fresh herbs.
Use an immersion blender to puree the sauce directly in the slow cooker until it reaches your preferred consistency. Or you can choice to leave sauce chunky.
Adjust seasonings to taste. Them serve and enjoy!