On sheet of waxed paper, combine flour, cocoa powder, baking powder, cinnamon and salt; set aside.
Using electric mixer, beat olive oil with sugar until smooth and light. Add eggs and egg yolk, one at a time, beating until smooth. Add milk and vinegar; beat until smooth. With mixer on low speed, gradually add flour mixture, beating until just combined. Stir in chocolate morsels with large spoon; cover with plastic wrap. Refrigerate at least 4 hours.
Heat oven to 325° F. Grease two large baking sheets with 1/2 tablespoon olive oil each. On lightly floured surface, divide dough into quarters. Roll each piece of dough into log, about 1 1/2 inches in diameter. Place logs on baking sheets, leaving space in between. Bake about 30 minutes, or until golden and set. Transfer to rack; let cool 10 minutes.
Reduce oven temperature to 300° F. On cutting board using serrated knife, cut each log into 3/4-inch-wide slices diagonally. Place slices, cut-side down, on baking sheets. Bake 15-18 minutes, or until toasted. Transfer to racks; let cool.