• Preheat oven to 325℉.
• Line a large cookie sheet with parchment paper. Set aside.
• In a medium bowl, whisk together the flour, cocoa powder, and salt. Set aside.
• In the bowl of a stand mixer, beat the butter and sugar on medium speed until light and fluffy.
• Add the sourdough starter and the vanilla extract and continue to mix until combined.
• With the mixer set to low speed, slowly add the flour mixture and mix until fully combined.
• Transfer the dough a work surface and place on a large sheet of parchment paper. Use a rolling pin to roll out the dough until about ⅛ inch thick.
• Use a 1½ inch cookie cutter to cut out as many cookies as you can from the dough. Collect the scrap pieces and re-shape into a ball. Continue to roll the dough out and cut out more cookies until you have used it all.
• Transfer the cookies to the baking sheet, spacing ½ inch apart. You will likely make several batches to fit all the cookies.
• Bake in preheated oven for 12-14 minutes.
• Allow to cool completely on cooling rack before filling with cream filling.

To Make the Cream Filling

• Use a stand mixer fitted with the paddle attachment to beat the butter, vanilla, and powdered sugar together until light and fluffy.
• Spread a small spoonful of cream between two cookies and gently press together until they just hold.