There's a chance that this was the original Christmas cookie, as the recipe is said to have originated over 300 years B.C. A first-century text lists the ingredients as rye flour, cumin, cheese, anise and eggs. In the 2000-plus years since, it has evolved into a chocolate nut cookie rich with warm winter spices.
Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper.
In a small bowl, whisk together the eggs, heavy cream, olive oil and orange zest.
Put the flour, sugar, walnuts, cocoa powder, baking powder, cinnamon, cloves, nutmeg and salt in the bowl of a food processor, and pulse until the walnuts are in medium-sized pieces. Add the egg mixture and chocolate chips, and continue to pulse until a thick dough forms.
Roll pieces of the cookie dough into golf ball-sized pieces, and arrange on the prepared baking sheets at least 3 inches apart. Bake, rotating halfway through, 15 to 17 minutes.
Transfer the cookies to a wire rack to cool completely, 20 minutes. Store in an airtight tin for up to 1 week, or freeze for 2 months. Dough can also be prepared and frozen up to 3 months ahead of time.