Preheat oven to 350°

In a large bowl or stand mixer, combine first 6 ingredients (flour through chocolate)

In a small bowl combine milk, eggs and egg white, and vanilla and add to dry ingredients

Mix to combine. Dough will be crumbly and dry

Pour out onto lightly floured board and knead 6 or so times to bring it together

Roll dough out into a log about 16” long

Place on a baking sheet covered with parchment paper

Gently flatten the roll to 1” thickness

Bake for 30 minutes

Remove roll to a wire rack to cool for 8 minutes, leaving the parchment on the baking sheet

With a serrated knife gently slice the roll on a diagonal into 1/2” slices, don’t worry too much if the edges crumble a bit

Reduce the oven heat to 325°

Lay the slices face down back onto the baking sheet and bake for 10 minutes, flip them over and bake another 10 minutes

Remove from oven and place on a wire rack to cool, they will continue to harden as they cool