For the Pastry: In a large bowl, cream together the butter/margarine and sugar until light and fluffy. Sift in the flour and mix to create a soft dough, using your hands to bring it together when necessary. Gently knead the dough on a clean surface to ensure it is completely combined, before wrapping the dough in cling film and placing in the fridge for 30 minutes to firm up a little.
Pre-heat your oven to 180°c (160°c for fan assisted ovens or Gas Mark 4). After 30 minutes, remove your dough from the fridge. Grease a 12-hole cup bun tray with a little butter/margarine and set aside.
Roll your dough to about 5mm thick and using a round cutter which is a little bigger than the cups on your bun tray, cut 12 circles. Carefully transfer each circle to your pre-greased tray, gently ensuring no air is caught underneath each and pressing the bottom and edges into place.
Prick a few holes into the bottom of each pastry cup, before lining them and filling with some baking beans. Bake for about 15 minutes, remove the baking beans and bake for a further 5 minutes, until the pastry cases are golden in colour. Allow to cool a little before adding the fillings.
For the Jam: Drain the juice from your tinned pineapple into a pan. Add the sugar to the pan. Roughly chop the pineapple slices before also adding to the pan. Bring the mixture to a boil and allow to boil for 20-30 minutes, watching closely and stirring often. After which time it will still be slightly syrupy but the pineapple will have darkened in colour. Transfer the jam to a sterilised jar and allow to cool completely before using in Pineapple Tarts.
Spoon a heaped teaspoon of jam into each pastry casing.
For the Cream Filling: In a large bowl, whisk the cream and icing sugar. If using an electric whisk, stop just before you think you have whisked enough - it's very easy to over-whisk cream with an electric whisk. Transfer the cream to a piping bag and pipe about a ping-pong ball amount of cream onto the top of each jam-filled pastry casing. Place into the fridge whilst you prepare the icing.
For the Yellow Icing: In a bowl, mix the icing sugar with the water, adding a little at a time. You want a just pour-able consistency. Add the yellow food colouring to create your desired stage. Starting with just a teaspoon, pour a little icing on top of the cream. Allow the icing to set before serving.