Line an 8x8-inch baking dish with parchment paper.
In a saucepan over low heat, melt the butter and chocolate chips together until smooth.
Stir in the peanut butter, vanilla, and a pinch of salt. Mix until well combined.
Remove from heat and let it cool for 5 minutes.
Fold in the mini marshmallows and chopped nuts.
Pour the mixture into the prepared dish and spread evenly.
Chill in the refrigerator for at least 2 hours, or until set.
Cut into bars and enjoy!