Measure first five ingredients into a saucepan.
Stir constantly until mixture boils.
Boil with stirring for about 7 minutes or to the soft-ball stage (250F).
Cool the pan slightly in a dish of cold water.
Add vanilla and beat until creamy.
Scrape into a greased 7x7-inch pan.
Mark into 36 squares and cool overnight.
Cut fudge into pieces and separate to dry surfaces slightly.
Wrap each piece in plastic film before packing in jars or boxes.