In a medium saucepan, stir together 3/4 cup sugar and 2 tablespoons cornstarch. Add 1 tablespoon orange zest and 3/4 cup orange juice. Cook and stir over medium heat until thickened and bubbly. Gradually stir about half of the orange mixture into 6 lightly beaten egg yolks. Return egg mixture to saucepan. Cook and stir over medium heat until mixture comes to a gentle boil. Cook and stir for 2 minutes more. Remove from heat. Stir in 1/2 cup cut-up butter until butter melts. Transfer to a bowl. Cover surface with plastic wrap. Chill for at least 1 hour. To store, place the prepared curd in an airtight container; cover. Store in the refrigerator for up to 3 days. Makes 1 1/2 cups.
A round cookie cutter with scalloped edges is a nice shape for these cookies, but bell, tree or star cutters are also good choices.
Store unfilled cookies in an airtight container at room temperature for up to 3 days or frozen for up to 3 months.