01 -
Heat the oven to 350°F and line baking sheets with parchment.
02 -
Whisk flour, baking powder, salt, cocoa and optional espresso powder together once.
03 -
Beat eggs, the extra yolk, sugar, oil and vanilla until frothy. Melt butter and the cup of chocolate chips gently, stirring until smooth.
04 -
Cool the chocolate mixture until warm rather than hot.
05 -
Fold it into the egg mixture.
06 -
Add the dry mixture and fold just until combined. Scoop tablespoon-size portions onto cool lined trays with about two inches between them.
07 -
Add optional extra chips and a light sprinkle of flaky salt.
08 -
Bake about eight to ten minutes, continuing as needed until tops are crackled and set without liquid centers. Rest five minutes on the tray before transferring carefully to a rack.