Cream butter and powdered sugar with an electric mixer until fluffy. Add egg white, vanilla extract, and orange zest and mix on medium speed until egg white is incorporated.
Add flour, one cup at a time, until just mixed. Shape the dough into a disc and wrap in plastic wrap. Chill in the refrigerator for 2 hours.
Preheat oven to 350°F.
Line baking sheets with parchment paper.
Roll dough onto a floured surface, ½-inch thick.
Cut into shapes and place cookies on baking sheets.
Chill in freezer for 10-15 minutes.
Bake for 12-15 minutes, until the edges of the cookies begin to brown.
Cool on wire racks for 30 minutes.
CHOCOLATE TOPPING:
Melt dipping chocolate according to package instructions.
Spoon chocolate onto each cookie and spread evenly. You can also dip the tops of the cookies into chocolate.
Let cookies sit for 15 minutes, until the chocolate hardens.