Here is an iconic cookie that is beyond delicious with it's giant size and soft and cake like consistency. Take a bite and you will have a great cookie experience. Enjoy!
Preheat oven to 350 degrees. Line two rimmed cookie sheets with parchment paper or silpat baking mat. Whisk flour, baking powder, baking soda, and salt in a large mixing bowl. Set aside. Using a hand held mixer or a stand mixer with the paddle attachment, cream together the sugar and softened butter until light and fluffy. This will take about 2 to 3 minutes. Add in the beaten egg, sour cream, vanilla extract, lemon extract if using. Beat until combined. Stop and scrape down sides of bowl if needed. Gradually add in the flour mixture. Using a large serving spoon is how I find to be the easiest way. Mix about 1 minutes. Stop scrape down the sides of bowl and beat again until completely combined. Another 20 seconds. Stop and continue to combine by hand with a rubber spatula. Batter will be very thick. Using a 1/4 cup measuring cup, lightly mist the cup with cooking or baking spray. Scoop and gently drop batter onto baking sheet. 5 to 6 mounds at a time. Make sure they are spaced. If you can get all 6 on the sheet that would be best. Bake between 15 and 18 minutes or until edges of each cookie are lightly browned. The cookies will stay light with just a hint of color. The tops should spring back lightly when gently touched. Let cookies cool on baking sheet for about 5 minutes. Then, slide the parchment paper onto the cooling rack for the cookies to cool completely.
In a medium mixing bowl, stir together all icing ingredients except the cocoa powder. I used a small whisk to get out any lumps and to make a smooth and shiny glaze. If needed add a teaspoon of water for consistency or more powdered sugar to thicken up a little. The icing should be pourable yet not too runny. You want the icing to be spreadable but not as thick as a frosting would be. Take half of the prepared icing and pour into a separate bowl. Add in the sifted cocoa powder. Using the whisk again, mix until smooth and spreadable. If needed add more water a teaspoon at a time for powdered sugar for right consistency. Turn cookies flat side up. So the rounded side is facing down. Hold one cookie in your palm, Using a butter knife or an offset spatula, start with the vanilla icing. Spread a layer of icing on only half of each cookie. Lay that cookie down and go on to the next. When finished with the vanilla icing, start spreading the chocolate over the other half of each cookie. Let set up completely. Once the cookies are completely dried and set, you can wrap them in plastic wrap like they do in the diners and bagel shops. Best stored in a sealed glass container up to 3 days on the counter. Can be refrigerated up to 5 days or frozen up to a month.