Line 13x9 inch pan with parchment paper.**
Microwave butter on high for 1 minute in very large glass microwavable bowl. 
Add sugar and evaporated milk, stirring well. 
Microwave on high for 5 minutes. 
Stir well. 
Microwave on high for 5 minutes. 
Stir well. 
Microwave on high in 1 minute increments for up to 5 more minutes until soft ball stage and caramel-colored.*** 
Add peanutbutter, marshmallow creme, and vanilla. 
Mix well and pour into pan immediately. 
Let set up at room temperature. 
When it's beginning to set up, you can lift fudge out of pan using the parchment paper lining. 
When completely cooled, cut into 1 inch squares.

*For Microwave Chocolate Fudge, substitute one 12 ounce package of chocolate chips and add 1 cup nuts.
**Rather than lining the pan with parchment paper, you can just butter the pan. 
***I have a small, cheap microwave, have been making this fudge for 20 years, and just microwave 5 more minutes without checking every minute, but when I tried to do that in my mom's 30 year-old microwave, it got brown (rather than caramel colored) and slightly burnt.