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1
Preheat oven to 375 degrees F. Line a baking sheet with parchment paper or a silicon baking sheet.
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2
Put the unsweetened and semisweet chocolates and butter in a medium microwave-safe bowl; heat at 75 percent power until softened, about 2 minutes.
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3
Stir, and continue to microwave until completely melted, about 2 minutes more.
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4
(Alternatively, put the chocolate and butter in a heatproof bowl.
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5
Bring a saucepan filled with an inch or so of water to a very slow simmer; set the bowl over, but not touching the water, and stir occasionally until melted and smooth.)
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6
Whisk the sugar, eggs and vanilla into the chocolate mixture until smooth.
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7
Sift the flour, cocoa, baking powder and salt into another bowl.
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8
Gradually whisk the dry ingredients into the wet ingredients until moistened.
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9
Switch to a rubber spatula and finish folding the batter together; take care not to over-mix.
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10
Use a small cookie scoop or spoon to drop a heaping tablespoon of batter onto the prepared pan.
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11
Repeat to make 36 cookies, spacing them about 1-inch apart.
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12
Bake until the cookies spring back when lightly touched, about 6 minutes.
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13
Cool the cookies slightly.
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14
Transfer half of the cookies to a rack.
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15
Turn the remaining cookies on the pan over, so they lay flat side up.
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16
Place a marshmallow on top of each flipped cookie and return pan to the oven.
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17
Cook just until the marshmallow begins to soften and puff, about 3 minutes.
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18
Cool marshmallow topped cookies slightly, about 2 minutes.
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19
Top with the remaining cookies, pressing lightly to make sandwiches.
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20
Cool whoopee pies completely on wire racks.
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21
Serve.
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22
Store in tightly sealed container for up to 1 week.
