This recipe is from the Ball Blue Book Guide to Preserving. Using “paste” tomatoes such as San Marzanos are ideal because of their low moisture levels. Quickly blanching the tomatoes (boiling them until the skins split then transferring them into ice water) helps to remove the skin efficiently. A quick squeeze of the peeled tomatoes can release most seeds. Processing with a food mill can help remove any skins or seeds you didn’t catch and will give the ketchup the right consistency. This homemade ketchup tastes divine and has quite a bit less sugar and salt than the store-bought kinds.