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1
Preheat the oven to 350 degrees F. Spray three 8-inch round cake pans with cooking spray. Line the bottoms with parchment paper.
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2
In a medium bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt.
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3
In a large bowl, whisk together buttermilk, sugar, stevia, oil, eggs, and vanilla. Fold in dry ingredients in 3 parts, alternating with coffee in 2 parts.
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4
Divide batter equally between the cake pans and bake, rotating the pans halfway through baking, until a toothpick inserted in the center of the cakes comes out clean, 17 to 20 minutes.
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5
Let cakes cool in the pans for 10 minutes, then remove from the pans and let cool completely on a rack, at least 45 minutes.
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6
In a large bowl or the bowl of a stand mixer fitted with the whisk attachment, combine peanut butter and butter. Beat on medium speed, scraping down the sides of the bowl frequently, until very smooth. Add stevia, powdered sugar, and cornstarch and beat until smooth and combined. Gradually beat in cream and vanilla until frosting is light-colored, smooth, and fluffy.
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7
Place 1 cake layer on a cake stand or serving plate. Top with 1/3 of the frosting and spread evenly to the very edge of the cake. Top with the second cake layer and 1/3 of the frosting. Top with the final cake layer and remaining frosting, spreading it smoothly to the edge of the cake, leaving the sides bare. Sprinkle peanuts in a 1-inch wide ring around the top outer edge of the cake, and sprinkle a few in the center.
