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1
Preheat oven to 350u00b0 F and line two baking sheets with parchment paper
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2
In a small bowl, whisk the flour, baking soda, and salt together.
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3
In the bowl of a stand mixer, beat the butter and sugar until creamy. Add in the vanilla extract and egg and mix until well combined. Scrape down the bowl.
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4
Alternate adding in the flour mixture and buttermilk in 3 additions. Mix until just combined.
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5
Use a tablespoon measure (or pastry bag) to portion the cookies 1 inch apart on the baking sheets. Bake the cookies for 6 to 8 minutes, or until the tops spring back when pressed gently and the cookies are a light golden brown around the edges. Cool completely.
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6
While the cookies are cooling, prepare the icing by whisking the confectioner's sugar, corn syrup, lemon juice, vanilla, salt, and water together until very smooth. Remove half of the mixture to another bowl and whisk in the cocoa powder and espresso powder until very smooth. Add a few drops of water to the chocolate icing until it is a spreadable consistency. The icing should be thin enough that it is easily spreadable, but not runny. If it seems dry, add water 1/2 teaspoon at a time; if it is runny, add confectioner's sugar 1 tablespoon at a time.
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7
Flip the cooled cookies so their flat sides are up. Use an offset spatula or knife to spread vanilla icing on half of the cookies, then spread chocolate icing on the other half.
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8
Let icing set for a few minutes, then dig in. Store the leftover cookies in an airtight container at room temperature for up to two days.
