These instructions apply for any of the four varieties of Marshmallow Bars. First, line a 13- × 9-inch pan with parchment paper.
Place the first three ingredients in a medium saucepan. Heat over medium heat, stirring frequently, until melted, combined and smooth.
Remove from the heat and stir in the vanilla. Let cool until just warm, but not so hot as to melt the marshmallows in the next step.
Place the remaining ingredients in a large bowl. Pour in the peanut butter mixture, stirring to coat completely.
Pour into the prepared pan, spreading evenly. Refrigerate for 2 to 3 hours, then slice into 24 bars.
Store in an airtight container in layers, with parchment or waxed paper between each layer, in the fridge for up to 5 days or in the freezer for up to 3 months.