Combine butter, caster sugar and vanilla extract in a microwave safe bowl.
Add condensed milk – do not stir.
Microwave on high for about 10 minutes (stop every minute to stir – so 10 times in total) or until golden brown. Keep watch in case it boils over (open the door and it will deflate again) and be careful: it will be HOT!!!
Allow to cool slightly and beat with a wooden spoon until the fudge starts to set.
Pour into a tin lined with baking paper and allow to set before cutting into squares.
Mine was a bit gooey and didn’t come off the paper very well but then I put it in the fridge and it was easy to cut up and came off the paper with no problems. It tasted amazing!