The Preparation
Whisk together flour, cocoa powder, sugar, salt, and baking soda in a bowl.
Add softened butter and mix until combined and crumbly.
Add milk and vanilla extract, mixing until dough comes together.
Roll dough into logs, wrap in plastic, and refrigerate until firm.
Slice into thin rounds (about 1/4 inch thick).
Place on a parchment-lined baking sheet.
Bake at 350 degrees F for about 12 minutes.
Let cool completely on a wire rack.
