Using a non-stick pan, put the water on a low heat and melt in the butter. Add the sugar and bring to the boil. It is important to keep stirring all the time. Once it is boiling, stir in the condensed milk and simmer for 20 minutes. Again, keep stirring to avoid it sticking/burning. Take off the heat and beat vigorously for five minutes, adding the flavouring of your choice. Pour into a rectangular greased tin and once it is partly cooled, cut into bars (roughly 5 inches long by 1/2 inches wide). Once the tablet is cold, wrap the bars in waxed paper and store in an airtight jar or tin.