Ingredients:

  • 1 and 3/4 cups (219g) all-purpose flour, spooned and leveled
  • 1/2 teaspoon baking powder
  • 1/4 teaspoon baking soda
  • 1/4 teaspoon salt
  • 10 Tablespoons (142g) unsalted butter, softened to room temperature
  • 1 cup (200g) granulated sugar
  • 1 large egg, at room temperature
  • 2 teaspoons pure vanilla extract
  • 1/3 cup (80g) full-fat sour cream, at room temperature
  • 4 and 1/2 cups (540g) confectioners' sugar, sifted (measure before sifting)
  • 6 Tablespoons (90ml) whole milk
  • 2 Tablespoons light corn syrup
  • 1 teaspoon pure vanilla extract
  • 1/2 teaspoon salt
  • 1 cup (120g) confectioners' sugar, sifted (reserved from vanilla icing portion above)
  • 1 Tablespoon (15ml) whole milk
  • 3 Tablespoons (15g) unsweetened natural or dutch-process cocoa powder

Instructions:

  1. Preheat oven to 350°F (180°C). Line baking sheets with parchment paper or silicone mats.
  2. In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
  3. In a large bowl, cream butter and sugar until light and fluffy.
  4. Beat in egg and vanilla extract until combined. Scrape down bowl.
  5. Gradually add dry ingredients, alternating with sour cream, until just combined. Be careful not to overmix!
  6. Drop 1/4-cup mounds of dough onto prepared baking sheets, leaving ample space between cookies.
  7. Bake until edges are lightly browned.
  8. Let cookies cool on baking sheets briefly, then transfer to a wire rack to cool completely.
  9. Whisk together confectioners’ sugar, 6 tablespoons of milk, corn syrup, vanilla, and salt until smooth.
  10. Transfer 1 cup of vanilla icing to a separate bowl. Add remaining 1 tablespoon of milk and cocoa powder. Whisk until smooth.
  11. Spread vanilla icing onto half of each cookie on the flat side.
  12. Refrigerate iced cookies for 15 minutes, or until the vanilla icing is set.
  13. Spread chocolate icing onto the other half of each cookie.
  14. Allow the icing to set completely at room temperature before serving.