Preheat oven to 350 degrees and line 2 cookie sheets with parchment paper or silicone baking mats.
In a large mixing bowl, combine softened butter and granulated sugar and beat until fluffy. Add large egg, vanilla extract, and Princess Flavoring. Mix well.
In small bowl, mix together the all-purpose flour, baking soda, and cornstarch. Gradually add to butter mixture until combined.
Divide dough in half. Scoop out 6 equal balls. Slightly press each into a flat circle and dip tops into a bowl of decorating sugar. Place on prepared cookie sheet.
Bake in preheated oven for 10-12 minutes, or until lightly browned. Repeat for remaining dough. Makes 12 very large cookies.
Notes
*Unless otherwise indicated, all butter used on this recipe site is salted.