Heat up a large pot of water and prepare a bowl with iced water. Bring the water to boil and set iced water bowl close to the stove.
Slice a small x across the bottom of each tomato (not the part that attaches to the vine).
Working in batches of 3 or 4 tomatoes, add them to the boiling water for 25-30 seconds. You will see the skin starting to peel off where it's sliced.
Use a slotted spoon to take tomato out of the pot and into the ice bath. Once cooled after a few seconds, take them out onto the cutting board and peel the skin off with your hands. It should come off nice and easy.
To Make Pomodoro Sauce:
Dice onion and tomatoes and set aside. If you see a lot of juices running off the tomatoes, you can pour off some of them but not all. Peel, smash, and mince garlic cloves.
Preheat a Dutch oven over medium heat and add the olive oil.
Add onion and sauté until transparent and starts to soften. Make a little well in the middle and add garlic. Cook garlic just until fragrant.
Add in diced tomatoes and bring it all to a simmer. Lower the heat to medium low so the sauce gently simmers and let it cook for 30-40 minutes. Do not cover with a lid but make sure to stir from time to time.
Stir in salt, pepper, sugar, and minced basil leaves. Let the sauce cook another 5 minutes or so and then you can transfer it into a blender to blend until smooth. You can also use an immersion hand blender to blend the sauce.
Storing:
If not using the sauce right away, make sure to cool to room temperature before placing into the refrigerator.
Store Pomodoro sauce in a glass jar with an air-tight lid, in the refrigerator. Properly stored, the sauce should last 5-7 days.
Note: to help keep your sauce from spoiling faster, it's best to pour the sauce out of the jar instead of using a spoon to scoop it out.
Freezing:
To freeze the sauce, transfer cooled sauce into freezer friendly zip-top storage bag. (You can portions it into more than one bag.) Make sure to only fill it about 3/4 of the way full to allow room for the sauce to expand while it freezes. Seal well, label, and freeze for up to 3 months.
Video
Notes
Don’t cover with a lid – don’t cover the pot with the lid while cooking the sauce. Pomodoro sauce is usually a thicker sauce so you want to cook out the liquids and let them evaporate. The sauce flavor will also be richer if you let the liquids cook out.
Don’t rush! Let the sauce simmer for the full recommended time and if you want a deeper flavor, let it cook on low for up to 2 hours.
Avoid a blender explosion! When heat is trapped in a blender, it builds pressure that may cause the lid to pop off unexpectedly. Usually, there is a removable cap in the center of the lid to prevent this from happening. Some other types of blenders will have a flap you can open in a lid to let the steam escape. Make sure to open the flap or the cap in the lid to let the steam escape while blending.