Cream the butter, granulated sugar, powdered sugar, and orange zest in a stand mixer on medium-low speed for 1 minute until creamy and smooth.

Incorporate the egg and vanilla extract, mixing on low until fully combined without overmixing.

Gradually add kosher salt, cornstarch, all-purpose flour, cake flour, and chopped chocolate, mixing until a soft dough forms, about 1-2 minutes.

Chill the dough wrapped in plastic wrap for at least 2 hours or overnight.

Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.

Slice the chilled dough into 1/4-inch thick rounds and place on the baking sheet, spaced 1 inch apart.

Bake for 10-13 minutes until lightly golden around the edges; let cool on the baking sheet for 15 minutes.

Enjoy the cookies while warm, or serve them alongside your favorite beverage.