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1
Heat the oven to 350 degrees F and arrange the racks to divide the oven into thirds.
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2
Line 2 baking sheets with parchment paper and set aside.
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3
Combine the flour, cocoa, baking soda, and salt in a medium bowl and whisk to aerate and break up any lumps; set aside.
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4
Combine the butter and sugars in the bowl of a stand mixer fitted with a paddle attachment.
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5
Mix on medium speed until lightened in color and fluffy, about 3 to 4 minutes.
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6
Stop the mixer and scrape down the beater and sides of the bowl with a rubber spatula.
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7
Add the peanut butter, egg, and vanilla and mix on medium speed until smooth, about 1 minute.
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8
Reduce the speed to low, add the reserved flour mixture, and mix just until the dough comes together.
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9
Scoop 16 level tablespoons onto each prepared baking sheet.
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10
Roll each portion between your hands to form a smooth ball and place them back on the baking sheet about 1 inch apart.
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11
Bake both sheets for 8 minutes.
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12
Rotate the sheets from top to bottom and front to back and bake until the cookies are set around the edges but still soft in the center, about 6 to 7 minutes more.
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13
Remove the sheets to wire racks and immediately use the back of a round teaspoon or the end of a large-handled wooden spoon to make an indentation in the center of each cookie.
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14
Let the cookies cool completely on the baking sheets, about 10 to 15 minutes.
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15
Meanwhile, make the filling.
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16
Place the chocolate and peanut butter in a medium heatproof bowl; set aside.
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17
Place the cream in a small saucepan over medium heat and bring to a simmer.
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18
Pour over the chocolate and peanut butter and let stand until the chocolate softens, about 5 minutes.
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19
Stir until evenly combined and smooth.
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20
Fill the indentation of each cookie with about 1 teaspoon of the ganache filling, sprinkle with the peanuts, and let sit until set, about 1 hour.
