In a medium microwave - safe bowl, add in 1 cup chocolate chips and butter. Heat in microwave for 20 second increments, string in between until chocolate is mostly melted. Set aside to cool. (It's okay of chocolate seizes or hardens a bit.)
Meanwhile, in a large bowl, whisk together sugar, eggs, milk and vanilla. Whisk well until they're completely incorporated, light and airy.
Add in slightly cooled chocolate to the egg mixture. Whisk continuously until fully combined and smooth.
Add in flour, cocoa powder, baking powder, salt and espresso powder. Mix until evenly combined but do not over mix. Mixture will be very loose.
Fold in chocolate chips and crushed pretzels.
Set in freezer to harden a bit for at least 15 minutes.
Pre-heat oven to 325 degrees.
On a lined baking sheet, use a 1.5 tbsp scoop to form cookie dough balls and evenly space them out on prepared sheet.
Top each cookie with a few extra chocolate chips and pretzel pieces.
Bake for 8-10 minutes. Top with a sprinkle of sea salt on top of each cookie immediately once out of the oven. Let sit on baking sheet for 3 minutes before transferring to cooling rack.