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1
Special equipment: a 2 1/4-inch round, fluted cookie cutter
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For the cookies: Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper.
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3
In a large bowl, whisk together the flour, cocoa, salt and baking powder.
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4
In another large bowl using an electric mixer, beat the butter and granulated sugar on medium speed until fluffy, about 3 minutes.
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5
Add the yolks and beat until combined.
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Add the flour mixture to the butter mixture and beat until well combined.
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7
Divide the dough into 2 pieces.
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8
Lightly dust a piece of parchment with cocoa powder.
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9
Roll 1 piece of dough on the prepared parchment to between 1/4 inch and 1/8 inch thick.
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10
Using a 2 1/4-inch round, fluted cookie cutter, stamp out as many cookies as you can.
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Transfer the cookies to the prepared sheets.
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12
Roll and cut the remaining dough; you can reroll the scraps once.
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13
Chill the unbaked cookies for 10 to 15 minutes.
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14
Bake until the cookies are set and the tops look dry, 14 to 16 minutes, rotating the sheets halfway through cooking.
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15
Transfer the cookies to a rack to cool completely, about 45 minutes.
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16
For the filling: Beat the confectioners' sugar and butter with an electric mixer until smooth.
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17
Add just enough milk to make a creamy filling.
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Beat in the mint extract.
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When the cookies are cool, flip half of them over.
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20
Spread or pipe about 1 heaping tablespoon of the filling on the flipped cookies.
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21
Top with the other halves and press together gently.
