Heat butter in a saucepan over low heat. It will be sizzle and bubbly from the water content. After the moisture and the sound of the sizzle are gone, wait for 1-2 minutes until the milk solids from the butter turn brown and turn off the heat. Don’t let the pan unattended or you will end up with burnt butter instead of brown butter.

Transfer it to a heatproof mixing bowl and let it cool. Add in sugar and brown sugar and whisk until combined. Add egg, and vanilla extract.

Shift flour and baking soda into the mixing bowl, give it a stir then add ⅓ cup chocolate chips, stir again until just combined.

Slice croissant in a halves. Flatten 2 tbsp of cookie dough then put it inside of each croissant, add more chocolate chips then close the croissant. Place 2 tbsp cookie dough on top of the croissant, add some more of chocolate chips on top every cookie dough for a better looking crookie.

Preheat oven to 350ºF or 175°C. Put the crookie to a baking sheet then bake for 12 minutes until golden brown. Cool for 2-5 minutes before removing to wire racks to cool completely, sprinkle them with a sea salt. Enjoy!