Ingredient:

• 1-1/2 cups all-purpose flour
• 1/2 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/2 teaspoon salt
• 1/2 cup butter, softened
• 2/3 cup sugar
• 1 large egg, room temperature
• 2 teaspoons vanilla extract
• 1/3 cup sour cream
• ICING:
• 2 cups confectioners' sugar
• 1 tablespoon whole milk
• 1 tablespoon light corn syrup
• 1 teaspoon vanilla extract
• 3 tablespoons Dutch-processed cocoa