Step 1

Place tomato, oil and oregano in a large saucepan over medium-high heat. Bring to the boil. Reduce heat to medium-low. Simmer for 10 minutes or until tomato is tender and skin has separated from flesh. Set aside for 10 minutes to cool slightly. Remove and discard oregano.

Step 2

Preheat oven to 160C/140C fan-forced.

Step 3

Push tomato mixture through a fine sieve over a large bowl or jug. Discard seeds and skin. Add salt and citric acid to tomato puree. Stir well to combine. Divide mixture between 2 shallow baking trays with sides.

Step 4

Bake for 3 hours, stirring every 30 minutes and swapping position of trays between shelves, or until tomato puree becomes a thick, reddish-brown paste and liquid has evaporated. Allow to cool. Spoon into a 1-cup-capacity clean glass jar. Spoon extra oil evenly on top of paste in jar. Secure lid. Refrigerate for up to 1 month (see note) or freeze for up to 6 months.