Cream together the butter, sugar, vanilla extract, lemon zest, eggs and salt in a mixing bowl with the paddle attachment for about 3-4 minutes on medium speed.
In a separate bowl, whisk together the dry ingredients.
Add in the dry ingredient mix and the sour cream alternating between the two.
Start with approx. 1/4 of the flour mixture and mix until just combined. Then add 1/3 of the sour cream and mix again.
Continue this process until you have used up all of the dry mixture and the sour cream - make sure to scrape down the bowl and paddle frequently. Start and end with the dry mixture and there should be a total of 3 additions of sour cream.
Scooping and Baking
Scoop the dough using a muffin scoop or a 1/4 cup cookie scoop. *Note if you want this recipe to make 2 dozen, use a 1.5 tablespoon scoop and scoop two little balls of dough.
Place onto the baking lined baking sheet, make sure to give them quite a bit of space.
The dough is sticky so wet your hands as necessary to roll the dough into balls and then flatten.
Gently flatten the cookies until they are 1/2" thick. Then, with damp fingers, smooth out the edges of each cookie. This helps to prevent the "texture" from browning too quickly.
Bake the cookies for 12-15 min. Rotate the cookies after about 8 min to make sure they brown evenly. These cookies should stay relatively pale in color.
Allow the cookies to cool on the baking sheet for 5 min, then transfer the cookies to cooling racks and allow them to cool completely.
Icing
After the cookies have cooled fully (about 15-20 min). They are ready to be iced!
Whisk together the powdered sugar, meringue powder, and milk. Then slowly add in the lemon juice (you might not need it all). This icing should be relatively thick as you don't want it running off the edges of the cookies.
Using a spoon, spread a heaping tablespoon of icing onto the bottom/ flat side of each cookie. Place each cookie icing side up on a cooling rack and allow the icing to set and harden.
Notes
*These will last at least one week in an airtight container at room temp. However, they will dry out easily so make sure to keep that container sealed!
**If you can't find Wünder Creamery quark or use an unsweetened quark, I would add 25 g of sugar.