In a mixing bowl, cream together the butter and granulated sugar for 2–3 minutes, until light and fluffy.

Add the egg and vanilla bean paste, mixing until fully combined.

In a separate bowl, whisk together the flour, black cocoa, cornstarch, and salt.

Add dry ingredients to the wet mixture and mix until a soft dough forms.

Preheat oven to 350°F (177°C). Line baking sheets with parchment.

On a lightly floured surface or between parchment sheets, roll dough to 1/8 inch thickness for crisp Oreo-style cookies.

Cut into rounds (2 inches). Transfer to a parchment lined baking sheet, spacing cookies slightly. The chill for 20 minutes.

While chilling, preheat oven to 350°F (177°C). Bake for 10–12 minutes, or until the edges look set and matte.

Allow cookies to cool completely.

Beat the butter until smooth.

Add the powdered sugar ½ cup at a time. Add the vanilla and pinch of salt with the last ½ cup.

Beat until creamy and thick, 2–3 minutes.

-For a firmer, more Oreo-like filling, add 2–4 tbsp more powdered sugar.

Pipe or spoon filling onto the backside of one cookie.

Top with a second cookie and press gently to create a sandwich.

Let sit 10 minutes to set, or refrigerate for cleaner edges.