Name: Black and White Cookies
Prep time: 20 min
Cook time: 18 min
Total time: 2 h
Yield: 12 large cookies
Ingredients: 1 and 3/4 cups (220g) all-purpose flour (spoon & leveled) (or more as needed, see note)*; 1/2 teaspoon baking powder; 1/4 teaspoon baking soda; 1/4 teaspoon salt; 10 Tablespoons (145g) 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*; 5 and 1/2 cups (660g) confectioners' sugar, sifted (measure before sifting); 7 Tablespoons (105ml) whole milk, divided; 2 Tablespoons light corn syrup; 1 teaspoon pure vanilla extract; 1/2 teaspoon salt; 3 Tablespoons (18g) unsweetened natural or dutch-process cocoa powder*