Step 1Heat the oven to 350 degrees.
Step 2In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter and sugar until light and fluffy. Beat in the egg until fully incorporated, then beat in the vanilla, flavoring and salt. Slowly beat in the flour to form a smooth dough.
Step 3Roll out the dough to just under 1/4-inch thickness on a lightly floured surface or between 2 sheets of parchment paper to keep the dough from sticking. (The dough can also be made ahead of time and refrigerated or frozen in a sealable plastic bag until ready to use.) . Cut into desired shapes and space about an inch apart on parchment-lined baking sheets.
Step 4Bake the cookies until set and barely colored on the edges, 12 to 14 minutes (timing will vary depending on the size and shape of each cookie).
Step 5Cool before decorating with royal icing.
Step 1In the bowl of a stand mixer fitted with the whisk attachment, beat together the powdered sugar and meringue powder to combine. Slowly beat in the corn syrup and ¼ cup warm water over high speed until the icing is light and fluffy and forms stiff peaks, 4 to 5 minutes. This makes about 3 cups icing. Divide the icing and color as desired, thinning as needed with additional water.