Place chocolate, condensed milk and vanilla essence in the slow cooker.
Cook for approximately 1 hour on low, stirring every 10-15 minutes, until fudge has a 'crusty' skin on top. (If you have a candy thermometer, make sure it has reached 44 degrees Celsius - this also helped to let me know it was done and would set correctly!).
Add pineapple lumps and stir fudge vigorously until it is smooth and shiny. Pour into a shallow slice tin lined with baking paper and place in the fridge until set. Delicious!