Line an 8x8 or 9x9 pan with wax paper or parchment paper.
In a large bowl, combine melted butter, melted peanut butter, sweetener, vanilla, and salt. Stir in peanut flour until dough comes together (it will be like a dough, not like a batter).
Press dough firmly and evenly into prepared baking pan. To really get it even, cover it with more wax paper or parchment paper and use a flat-bottomed glass or measuring cup to press).
Set a heatproof bowl over a pan of barely simmering water, and add the chopped chocolate and butter. Stir until melted and smooth.
Pour over bars and use a knife or offset spatula to spread to the edges. Refrigerate 1 hour until set.
