Preparation

Make the cookies

• 将面粉，小苏打和盐筛入一个大碗中。
• In a stand mixer fitted with the paddle attachment or in a large bowl using a hand mixer, beat the butter and sugar on medium speed until light and fluffy, about 2 minutes. Add the egg and vanilla, and beat to combine. In three additions each, alternately add the dry ingredients and sour cream, beating after each addition. Beat on medium speed until well combined, taking care to not overmix the dough, which will be sticky.
• Divide the dough into three portions and wrap each portion in plastic wrap. Refrigerate for at least 8 hours and up to 24 hours before using for the flavors to develop. (Or freeze for up to 1 month and thaw overnight in the refrigerator.)
• Position racks in the upper and lower thirds of the oven, and heat to 400°F. Line 2 or more baking sheets with parchment.
• 大量面粉的工作表面和一个滚动销，然后将一块面团滚动到1/8至1/4英寸之间。快速工作，使面团保持冷，使用面粉切割机或刀切出形状。转移到烤盘上，将饼干间隔约1英寸。烘烤前冷藏至少30分钟。重复其余的面团，如果有的话，请重新卷来制作更多的饼干。
• Bake two sheets at a time, rotating and switching their positions halfway through, untilthe bottoms of the cookies are golden brown, 7 to 9 minutes. Transfer the cookies to a rack and cool completely before icing.

Make the icing

• Combine the confectioners’ sugar and salt in a large bowl. Melt the butter in a medium saucepan over low heat. Add the milk and bring to a boil over medium-high heat. Whisk in the sugar mixture, then the vanilla, and cool to room temperature. Add food coloring to batches of the icing, if you like, and then ice and decorate the cookies as you like. Store in a single layer for up to 2 days.