In a mixing bowl, whisk together flour, cornstarch, and powdered sugar.
Add the softened butter and mix until a soft dough forms.
Roll the dough into a log or flatten it into a disc, then wrap in plastic wrap and refrigerate for 30 minutes.
Preheat oven to 325°F (165°C) and line a baking sheet with parchment paper.
Roll out the dough to about 1/4-inch thickness and cut into desired shapes.
Sprinkle with pastel sanding sugar and place cookies on the prepared baking sheet.
Bake for 12-15 minutes, or until the edges are lightly golden.
Let the cookies cool on the baking sheet for a few minutes before transferring to a wire rack.
Serve and enjoy!