01 - Preheat oven to 325°F and line two baking sheets with parchment paper.
02 - In a large bowl, cream together softened butter and powdered sugar until light and fluffy.
03 - Add vanilla extract and mix to combine.
04 - In a separate bowl, whisk together flour, cornstarch, and salt. Gradually add dry ingredients to butter mixture, mixing until soft dough forms.
05 - Lightly flour work surface and roll dough to 1/4-inch thickness.
06 - Cut out cookies using round or flower-shaped cutter and transfer to prepared baking sheets.
07 - Gently press edible flower onto each cookie. Brush tops lightly with egg white to adhere flowers. Sprinkle with granulated sugar if desired.
08 - Bake for 12-15 minutes, until edges are just barely golden.
09 - Cool on baking sheets for 5 minutes before transferring to wire rack to cool completely.