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1
Preheat oven to 350 degrees F. Coat two baking sheets with cooking spray or line with parchment paper and set aside.
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2
In a large mixing bowl, use an electric mixer on medium spped to mix butter and sugar until well blended, about 3 minutes.
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3
Add eggs, one at a time, mixing until smooth after each egg.
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4
Mix in vanilla extract.
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5
In a separate bowl, stir together flour, cocoa powder, baking soda, and salt.
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6
Add half the flour mixture to mixing bowl and mix on medium speed until combined.
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7
Add half the buttermilk and mix again on medium until smooth.
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8
Repeat with remaining flour and buttermilk, and mix until smooth.
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9
Batter will be thick and slightly springy.
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10
Drop 2-tbsp portions of batter onto prepared baking sheets, leaving 2 inches between each portion to allow for spreading.
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11
Bake for 11-13 minutes, until puffed and set but still soft when touched lightly with finertips.
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12
Let cakes cool for 3 minutes on baking sheets before transferring them to wire racks to finish cooling, about 15-20 minutes.
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13
Repeat with remaining batter.
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14
Prepare filling while cakes are baking and cooling.
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15
In a large mixing bowl, use an electric mixer on medium speed to mix cream cheese, peanut butter, butter, vanilla, and salt until creamy.
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16
Add half the confectioner's sugar; mix on low at first to combine, then on high until smooth.
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17
Add remaining confectioner's sugar and milk and blend on low, then on medium until light and fluffy, about 3-4 minutes.
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18
Assemble whoopie pies.
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19
Spoon filling onto the flat sides of half the cakes, dividing it evenly among cakes.
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20
Top with remaining cakes, flat side against the filling, rounded side up.
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21
Serve immediately, or wrap each whoopie pie individually in plastic wrap and store at room temp for up to two days or in the freezer for up to two months.
