Melt the butter in a large saucepan over a high heat. Add the onions and cook for 5 minutes whilst stirring frequently with a wooden spoon. Add 2 tablespoons of water and scrape the bottom of the pan to lift the caramelised residue and browned bits. Continue to cook for a further 2 minutes.

Add another 2 tablespoons of water and repeat this method of adding water and then scraping for a total 15 minutes or until the onions are completely softened and have turned a deep, nut brown colour.

Add the tomatoes, castor sugar, light brown sugar, lemon juice, vinegar, Salt and NOMU Spanish Rub to the onions and stir to combine. Bring the mixture to a boil, reduce the heat and simmer, stirring occasionally, until the tomatoes have broken down and the jam has thickened and developed a nice thick consistency.

Remove from the heat, transfer the jam into two sterilised jars and seal.

Tip: A delicious addition to a cheese board! These jars also make great gifts for all sorts of occasions.