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1
Make the cookies:.
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2
Sift the flour and cocoa together into a medium bowl.
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3
Cream the butter and sugar on medium speed until light and fluffy, about 2 minutes.
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4
Add the vanilla and salt; continue beating until blended and smooth, about 1 minute more.
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5
Add the flour-cocoa mixture and mix on low speed until a soft dough forms, about 1 minute.
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6
Chill the dough until firm enough to roll into balls, 40 to 60 minutes.
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7
Heat the oven to 350F Line cookie sheets with parchment or nonstick baking liners.
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8
Roll heaping teaspoonfuls of the dough into 1-inch balls.
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9
Arrange them 2 inches apart on the lined sheets.
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10
With a lightly floured thumb or index fingertip, press straight down into the middle of each ball almost to the cookie sheet to make a deep well.
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(Or use the end of a thick-handled wooden spoon.
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12
).
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13
Bake one sheet at a time until the tops of the cookies look dry, 8 to 9 minutes.
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14
Gently redefine the indentations with the end of a wooden spoon.
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15
Let the cookies cool on the sheet for 5 minutes and then let them cool completely on racks.
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16
Make the filling:.
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17
Put the chocolate and butter in a heatproof bowl set in a wide skillet of almost simmering water.
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18
Stir with a heatproof spatula until almost melted, 2 to 4 minutes.
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19
Remove the bowl from the heat and stir until melted and smooth, about 30 seconds more.
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20
Stir in the mint extract.
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21
Let the filling cool, stirring occasionally, until slightly thickened and a bit warmer than room temperature, 30 to 40 minutes.
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22
Spoon the filling into a small pastry bag with a small plain tip.
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(Or use a small plastic bag and cut a tiny bit off a bottom corner of the bag.)
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24
Pipe the filling into the center of each cookie.
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25
Cool completely before serving or storing.
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26
The cookies will keep in an airtight container at room temperature for 4 to 5 days.
