In a large mixing bowl, add softened butter, brown sugar, granulated sugar, and salt. Using a hand mixer or stand mixer with fitted paddle attachment, beat until light and fluffy, about 2-3 minutes.
Add salt and vanilla and beat well until combined.
Add in heat-treated flour and mix until combined. Add milk, 1 tablespoon at a time, and mix. Add more milk, if needed, to reach a soft cookie dough consistency. Fold in chocolate chips.
Place cookie dough onto a flat surface or pan lined with parchment paper. Place another sheet of parchment paper on top of dough and then use a rolling pin to flatten dough into a thin slab. Remove top layer of parchment paper.
Add chocolate wafers or chocolate chips to a microwave safe bowl and microwave for 1-2 minutes or until chocolate is melted, stirring every 30 seconds so it doesn't burn.
Pour melted chocolate over cookie dough and then use a spatula or knife to spread it evenly over dough. Top with sea salt while the chocolate is still wet.
Refrigerate dough for at least 30 minutes to harden or let sit at room temperature. Once chocolate is hardened, use a knife to cut into pieces or break apart. Store in in an airtight container in the refrigerator.