Preheat oven to 325 degrees F.
Line 2-3 cookie sheets with parchment paper
In a bowl place the flour, salt and baking powder together. Mix to combine
In the bowl of a mixture, cream together the sugar and butter on medium speed. About 3-4 minutes
Scrape the borders and bottom of your mixer with a spatula
Add the eggs and the egg white on at a time and mix well after each addition
Pour in the vanilla extract
In 2-3 batches, add the dry ingredients
Cut the corner of a zip-top bag and insert a round piping tip on that corner (optional)
Add the cookie dough into the zip-top bag and pipe wide logs on the cookie sheet. Make sure they are separated as they tend to expand in the oven
Bake for 13-14 minutes or until browned on top
Remove from oven and let them cool on a cooling rack (they will get crunchy at this point)
Melt chocolate in a small saucepan
Spoon melted chocolate on the bottom surface of a cookie. Sandwich with another cookie
Let this mixture dry at room temperature
Enjoy!
Keep cookies fresh in an airtight container