- Using a small knife, remove the core from the tomatoes and chop the flesh. Place in a very large pot.
- Over medium-high heat, cook the tomatoes for 25 minutes, stirring often, or until softened. This first period of cooking will help purée the tomatoes through a manual (Tic Tac-style) or electric tomato press, or with a potato masher.
- Purée the tomatoes with your chosen press or masher. Compost or discard the tomato skins and seeds.
- Prepare the lids and jars (see note).
- In the same large pot used to cook the tomatoes, heat the oil. Add the tomato purée. Add aromatics at this point, if desired (see note). Do not add salt. Bring to a boil. Reduce the heat and simmer for 30 to 45 minutes (for a more liquid sauce that can be reduced when ready to use) or up to 1 hour 30 minutes for a thicker sauce.
- Add 2 tbsp (30 ml) of the lemon juice and 1 tsp of the salt to each 4-cup (1 litre) jar.
- Divide the tomato sauce among the warm jars, leaving at least ½-inch (1 cm) space at the top. Remove any air bubbles with a non-metallic utensil and wipe the rims of the jars with a clean dishcloth.
- Centre the lids (discs) on the jars and tighten the rings until the point of resistance, without forcing.
- Place the jars upright on a support rack in a pot of hot water. Make sure the jars are covered by at least 1 inch (2.5 cm) of water. Cover the pot. Bring to a boil over high heat. Once the water comes to a boil, calculate 40 minutes processing time.
- Remove the jars from the water.
In a small pot, place the lids and cover with cold water. Bring to a simmer, turn off the heat and leave the lids in the hot, but not boiling, water, in order to activate the rubber sealing band.
In a large pot, place the jars and cover with water. Bring to a simmer over medium heat. Adjust the heat to low and leave the jars in the pot while you prepare the recipe. Drain them just before filling with tomato sauce.
Feel free to add aromatics of your choice to this plain tomato sauce, such as garlic, basil leaves, bay leaves, oregano, etc. Do not add salt when cooking the tomatoes. The salt is added directly to the jars during the canning process.