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 degrees. 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 for about 30 minutes, or until golden and set. Transfer to rack; let cool 10 minutes.
Reduce oven temperature to 300 degrees. 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 for 15-18 minutes, or until toasted. Transfer to racks; let cool.
All materials courtesy of Family Features. Explore more tips and recipes using olive oil at filippoberio.com