Peel the pineapples and place in a food processor and blitz until fine.
Place everything into a heavy based large saucepan.
Bring everything to boil, then simmer for about 2 hours, until cooked right down, stirring every so often, especially towards the end, as you don't want it to burn.
You'll end up with a thick jam, a dark honey brown in colour.
Total cooking time depends on the amount of pineapple you use as well as how juicy it is, and therefore how much liquid needs to be cooked off. Nutritional info is just for the jam, in 150 pineapple tarts.