Get Ready to Bake: Preheat your oven to 350°F (175°C). Lightly grease a 9x9 inch baking pan, then line it with parchment paper, leaving a bit of overhang on two sides to easily lift the bars out later.
Mix the Base: In a large microwave-safe bowl, combine ½ cup of the peanut butter and ¼ cup of butter. Microwave in 30-second bursts until smoothly melted. Stir in the brown sugar substitute, egg, and 1 teaspoon of vanilla extract until everything is well combined.
Create the Batter: Add the almond flour, baking powder, and salt to the wet mixture. Mix thoroughly until a thick, even batter forms.
Bake to Perfection: Press this peanut butter batter evenly into your prepared pan. Bake for about 17-20 minutes, or until the edges turn golden brown. Let it cool in the pan for 10 minutes while you make the icing.
Whip Up the Icing: In another microwave-safe bowl, combine the remaining ½ cup peanut butter, almond milk, and 3 tablespoons of butter. Microwave for 30 seconds until melted and smooth. Immediately whisk in the powdered sugar substitute and ½ teaspoon of vanilla extract until the icing is creamy and lump-free.
Layer and Top: Pour the warm, creamy icing over the slightly cooled peanut butter bar base, spreading it out evenly. Sprinkle the chopped peanuts on top, gently pressing them into the icing.
Chill and Enjoy: Place the pan in the refrigerator for 1-2 hours, or until the bars are completely firm. Once chilled, use the parchment paper sling to lift the entire slab out of the pan. Cut into 16 delightful squares and enjoy your healthy, low-carb treat!