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1
Stir flour and baking powder together in a bowl.
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2
Beat butter and white sugar together in the bowl of a stand mixer using the paddle attachment until light and fluffy, about 3 minutes. Add egg and vanilla extract; beat 1 minute more. Slowly add flour mixture and blend until dough begins to pull away from the sides of the bowl.
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3
Turn dough onto a piece of parchment paper. Knead dough a few times using your hands and form into 2 discs. Wrap each dough disc in plastic wrap and refrigerate for 2 hours.
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4
Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with a silicone mat.
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5
Remove 1 disc of dough from the refrigerator. Place dough on a lightly floured work surface; top with a piece of parchment paper. Roll out dough to about 1/3-inch thickness. Cut dough with round cookie cutters and transfer to the prepared baking sheet.
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6
Place baking sheet with cookies on it in the freezer or refrigerator for 3 to 5 minutes.
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7
Bake in the preheated oven until cookies are just barely beginning to turn golden brown, 8 to 10 minutes. Cool cookies on the baking sheet for 1 minute; transfer to a wire rack to cool completely. Repeat with second disc of dough.
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8
Wipe down all equipment for making the icing with vinegar, including spatulas, measuring cups, and bowls.
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9
Combine confectioners' sugar and meringue powder in the bowl of a stand mixer using the paddle attachment.
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10
Mix water, corn syrup, and clear vanilla extract together in a separate bowl. Pour water mixture into sugar mixture and beat on medium speed until stiff peaks form in the icing, 4 to 5 minutes.
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11
Decorate cooled cookies with icing.
