In a large mixing bowl, cream the butter, granulated sugar, and light brown sugar on medium speed until light and fluffy. Blend in vanilla extract and the zest of one orange.

Gradually add in the all-purpose flour while mixing on low speed. Mix until just combined, then fold in dark chocolate chips and remaining orange zest.

Divide the dough into two logs, wrap in plastic wrap, and refrigerate for at least 2 hours.

Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper. Unwrap one log, brush with egg wash, and roll in turbinado sugar.

Slice dough into 1/2-inch thick cookies, place on baking sheet and bake for 12-14 minutes until edges are golden.

Let cookies cool on the baking sheet for about 10 minutes before transferring to a wire cooling rack.