Line an 8x8 baking dish with foil so that it is hanging over edges , so you can lift fudge out of pan after firm-butter foil or spray well with food release
In a sauce pan over medium high heat add sugar, milk and butter stirring constantly until sugar and butter melt and come to boil. Reduce heat and let boil stirring occasionally until soft ball stage (4-6 minutes)
Remove from heat, beat in peanut butter and vanilla - when smooth pour into pan
Freeze or refrigerate for 1-2 hours - cut and serve