• Set oven racks in the middle of the oven then preheat the oven to 350 degrees. 
• In a medium mixing bowl, combine the dry ingredients of flour, baking powder, baking soda, and salt and set aside. 
• In the bowl of a stand mixer, add room temperature butter, and sugar, and with a paddle attachment, mix at medium speed until light and fluffy (about 2 minutes). Add egg and vanilla extract and beat until just combined. 
• At low speed, add half of the flour mixture, alternating with sour cream, scraping sides of the bowl with a rubber spatula as needed. Give one more good stir to make sure everything in the bottom of the bowl is incorporated. 
• Now it’s time to line baking sheets with parchment paper. 
• Grab a ¼ cup cookie scoop and drop cookie dough 3-inches apart on the prepared baking sheet pans.
• Bake for 15-18 minutes until the edges of cookies are slightly brown, rotating your pan halfway through baking. 
• Remove sheet pans from the oven and place them on a wire rack. Let cookies cool on the pan for 5 minutes, then remove them to the wire rack to cool completely.

Cookie Icing

• Whisk confectioners sugar, 6 Tablespoons milk, corn syrup, vanilla, and salt together in a bowl until smooth. Remove 1 cup of glaze to a small bowl and set aside. 
• In the reserved bowl, whisk in the cocoa and the remaining tablespoon of milk to create chocolate icing.

To Frost Cookies

• Working with one cookie at a time, spread vanilla icing on half of the flat side of each cookie with an offset metal spatula. Let icing set for about 15 minutes or put in the fridge to speed up the process. 
• Now spread the remaining half of the cookie with chocolate icing and let sit until the icing is firm. If you want a neat line between the vanilla and chocolate, cover the vanilla with a piece of wax paper before adding the chocolate frosting. Then carefully peel off to create a perfect edge. 
• Cookies may be stored at room temperature for up to 2 days.