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1
Preheat oven to 350 F. Line cupcake pans with paper liners.
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2
Whisk the cocoa powder and water together in a small bowl then set aside. In a medium bowl, whisk the flour, baking soda, baking powder and salt together.
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3
Add the butter and sugar to a medium saucepan. Set over medium heat and cook, stirring occasionally, until the butter is melted. Pour the buter/sugar mixture into the bowl of a stand mixer and beat on medium-low speed for 4-5 minutes, or until the mixture is cooled. Mix in the eggs, one at a time, and beating well after each addition. Add the vanilla, then the cocoa mixture and beat to incorporate. With the mixer on low, alternately add the dry ingredients (in 2 additions) with the sour cream (in 1), beating until just combined.
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4
Divide the batter between the prepared cupcake liners, filling them about 2/3-3/4 full. Bake for 18-20 minutes. Transfer the pans to wire racks and let the cupcakes cool for about 5 minutes before removing them to the racks to cool completely.
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5
Filling:
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6
Combine the dulce de leche, peanut butter and 1/4 cup heavy cream in a small saucepan. Set over medium-low heat and warm, whisking frequently, until the ingredients are combined and the filling is smooth. If the filling is too thick, add additional cream to the pan and whisk to incorporate. The filling will thicken as it cools so keep that in mind.
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7
Use a small paring knife to cut a cone-shaped piece from the center of each cupcake. Fill the hole with the peanut butter dulce de leche, then replace the top portion of the cone (you'll need to slice off the tip).
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8
Icing:
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9
Add the confectioners' sugar, peanut butter, butter, vanilla and salt to the bowl of a mixer. Beat on medium-low speed until creamy. Scrape down the sides of the bowl, then add the heavy cream and beat the icing on high speed until it is light and fluffy.
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10
Pipe frosting into a swirl on each cupcake then garnish with chopped peanut butter cups, if desired.
