Using a serrated knife, slice your pure butter croissant in half and set aside.
In a medium bowl, mix the room temperature butter, egg and vanilla. Add your flour, pudding mix, baking soda, corn starch, salt and dark chocolate chips. Mix on low until just combined.
Place the bowl with the cookie dough in the refrigerator for about 15 minutes to chill.
For large croissants, like the ones from Trader Joes, place 2-3 cookie scoops worth of dough in the center of the bottom croissant half. Be sure to leave a little bit of an edge around the cookies to ensure the dough doesnt spill out of the croissant while baking.
Place the top half of croissant over the cookie dough. Roll up 2-3 quarter sized balls of dough and press them gently onto the center of the top half of the croissant.
Place the crookie onto a parchment lined baking sheet and bake for 12 minutes.
Allow the crookie to cool slightly and then dust with powdered sugar before serving