In a saucepan, add the sugar and milk and bring to a boil. Boil 2-3 minutes, stirring. Remove from heat and stir in the peanut butter and vanilla until smooth. Add in the peanuts and stir.
Pour the peanut butter mixture into the prepared pan and smooth. Let cool completely and chill 1 hour. Slice and serve.
Notes
If you prefer a smoother fudge, leave the peanuts out.
Leave in a airtight container to keep these fresh.