Confit comes from the French word for "preserve," confire. For tomatoes, that means baking them at a low temperature with basil, garlic, and olive oil.
Preheat oven to 350 degrees. Bring a large pot of water to a boil over medium-high. Prepare an ice bath.
Score a shallow X in the bottom of each tomato with a knife, then place in boiling water for about 10 seconds. With a slotted spoon, transfer tomatoes immediately to ice bath. When cool, remove and peel tomatoes by gripping the skin between your thumb and the flat part of a knife blade, starting at the scored X.
Combine tomatoes (cored-sides down), basil, and garlic in a shallow baking dish. Sprinkle generously with salt; drizzle with oil. Bake until tender, about 50 minutes. Let cool completely.
Transfer tomatoes with their juices to quart-size glass jars, leaving 1/2 inch of headspace. Freeze until ready to use, up to 1 year.