Pour the milk into a heavy-based saucepan and bring slowly to the boil. Add the sugar and butter. Heat slowly, stirring all the time, until the sugar dissolves and the butter melts. Bring to the boil, cover and boil for 2 minutes.

Uncover, and continue to boil steadily, stirring occasionally, for 10 - 15 minutes, until a little of the mixture, dropped into a cup of cold water, forms a soft ball when rolled between finger and thumb.

Remove from the heat. Stir in the vanilla flavouring. Leave to cool for 5 minutes.

Beat the fudge until it just begins to lose its gloss and is thick.

Transfer to a buttered 18 cm (7 inch) square tin. Mark into squares when cool. Cut up with a sharp knife when firm and set. Store in an airtight container.