Well oil an 11" x 7" shallow baking tin pan. Put the water and lemon juice in a heavy-based saucepan and heat until slightly warm.

Stir in the sugar and continue to heat gently, stirring with a wooden spoon, until all the sugar has been thoroughly dissolved. Don't allow it to boil.

Stir in the cream of tartar and bring to the boil to 242F on a sugar thermometer (or until a teaspoon ful of the mixture forms a soft ball when it is dropped into a cup of cold water).

Remove from the heat and beat in the butter. Return to the heat and boil to 280F or when a teaspoon of the mixture forms a thin thread when dropped into a cup of cold water. (The thread will bend and break when pressed between the fingers)

Remove from the heat and beat in the vanilla extract. Pour into the oiled tin and leave until it is almost set.

Then mark into small rectangles with a knife.

When it is competely set, break into pieces and store in an airtight container.