Butter 8 in. non-stick baking dish and set aside.

In a medium sauce pan over medium heat, heat butter and peanut butter until the mixture comes to a boil. Remove from heat.

Add the salt and vanilla extract, then stir in the powdered sugar until smooth (no lumps)

Pour the fudge mixture into the prepared pan and smooth the top.

Press a piece of plastic wrap directly on the fudge and refrigerate until set, about 1 1/2 hours

Cut into squares and serve.