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1
For the cookies: Sift the flour, granulated sugar, cocoa powder and baking soda together in a medium mixing bowl and set aside.
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2
Whisk the butter, milk and egg yolk together in a separate bowl until uniform in color and texture.
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3
Add the butter mixture to the flour mixture and stir until it forms a dough.
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4
Divide the dough in half and place each half onto a sheet of plastic wrap or parchment paper.
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5
Form into two logs about 1 to 1 1/2 inches in diameter.
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6
Refrigerate for at least 4 hours to overnight.
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7
Preheat the oven to 375 degrees F. Line 2 baking sheets with parchment paper.
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8
Remove one dough log at a time from the refrigerator.
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9
Slice into 1/4-inch-thick slices and place onto the baking sheets.
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10
Bake until firm and set, 8 to 10 minutes.
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11
Set aside on a rack to cool.
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12
Repeat with the second log.
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13
For the banana filling: Add the butter and shortening to a small bowl and beat with an electric mixer on medium speed until combined, about 1 1/2 minutes.
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14
Reduce the speed to low and add
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15
the confectioners' sugar in two batches.
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16
Add the extracts and mix until combined; set aside.
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17
Slice the banana into 3 dozen 1/8-inch-thick slices.
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18
To assemble the cookies: Place a heaping 1/2 teaspoon filling on each cookie.
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19
Place a banana slice on the filling, making sure it does not overlap the edge, and then cover with another cookie and press down gently.
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20
For the bittersweet ganache: Pour a couple inches of water into the saucepan and heat over medium-low heat to just below a simmer.
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21
Put the chocolate and shortening in a metal bowl and place over the hot water to melt, stirring often.
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22
If the water starts to steam too much, remove the bowl from the pan to avoid scorching the chocolate.
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23
When fully melted, remove from the heat, leaving the bowl of chocolate over the water.
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24
Using two forks, dip the sandwich cookies into the melted chocolate, turning gently to coat, and remove to wax paper.
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25
Allow to sit at room temperature until the chocolate is completely set, at least 2 hours.
