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1
To make the crust: Line a metal 13x9 baking pan with foil, leaving an overhang on opposite sides to lift the bars out.
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2
Stir the butter, sugar and salt together in a medium bowl. Add the flour and peanuts, mixing until a stiff dough comes together. Press the dough evenly over the bottom of the prepared pan. Use a fork to prick the dough all over, then refrigerate for about 30 minutes, or until the dough is firm.
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3
Meanwhile, preheat oven to 325 F.
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4
Bake the crust for 20 minutes, then decrease oven temperature to 300 F and continue baking for another 20-25 minutes, or until the crust is golden brown and set. Transfer pan to a wire rack and let the crust cool completely.
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5
To make the filling: In the bowl of a stand mixer fitted with the paddle attachment, beat the peanut butter and butter on medium until smooth. Add half of the confectioners' sugar, the vanilla extract and 1 tablespoon of hot water to the bowl. Starting on low speed, then increasing to medium, beat until smooth and fluffy. Mix in the remaining confectioners' sugar until smooth. The mixture should be thick but not too stiff - if it is, add another tablespoon of hot water.
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6
Using an offset spatula, spread the peanut butter filling over the cooled crust.
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7
To make the ganache: Add the chocolate to a heatproof bowl. Bring the heavy cream to a boil in a small saucepan then pour over the chocolate. Let stand for about 3 minutes, then stir gently until smooth.
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8
Spread the ganache over the peanut butter filling in an even layer. Let sit until the ganache sets (at least 3 hours at room temperature, or 1 hour in the fridge).
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9
Lift the bars out using the foil handles, then cut into squares before serving.
