In a medium bowl, combine butter, orange zest, vanilla extract, and powdered sugar. Beat until fluffy, about 2-3 minutes.

In a separate bowl, mix together flour and kosher salt. Gradually add this dry mixture to the butter mixture and mix until the dough appears shaggy.

Gently fold in chopped dark chocolate until well combined, forming a cohesive dough.

Place half of the dough on plastic wrap and shape it into an 8-inch log. Repeat with the remaining dough. Wrap tightly and chill in the refrigerator for at least 2 hours.

Preheat the oven to 350°F (175°C). Remove logs from the refrigerator and slice into ⅓-inch discs.

Line a baking sheet with parchment paper and arrange cookie discs. Bake for 13-15 minutes until edges are golden brown. Let cool on the baking sheet for a minute before transferring to a wire rack.