Line a 8x8 or 9x9 square baking pan with foil or parchment, then lightly grease the foil or parchment; set aside.
In a large heavy bottomed saucepan, combine the granulated sugar, marshmallow fluff, evaporated milk and cubed butter over medium heat. Bring to a boil, and cook, stirring constantly, for 5 minutes. Remove from the heat and stir in the peanut butter chips, peanut butter, and vanilla extract until combined and melted together.
Pour the fudge into the prepared pan and smooth into an even layer. Let stand for about 10-20 minutes to cool down some, then place in the refrigerator to chill and set, about 2 hours. Once chilled and set, remove from the pan and cut into squares, trimming off any rough edges with a sharp knife. Since this fudge is sticky, I recommend wetting your knife with HOT water, then wiping the water off and using the hot knife to cut, repeating after each cut. I got about 25 pieces of fudge, doing 5 rows by 5 rows (and trimming the edges). Place the squares of fudge onto a baking sheet lined with parchment and freeze until firm, about 20 minutes.
Melt your candy coating according to package directions, or until smooth. Use a fork to lower a piece of semi-frozen fudge into the candy coating and toss to coat. Allow excess chocolate coating to drip off of the fork, then carefully slide the coated fudge piece back onto the parchment-lined baking sheet. Repeat with coating the remaining fudge pieces. With any leftover chocolate, drizzle over the set chocolate fudge pieces, or top with sprinkles while coating is still wet.