Make the flowers:
With a fork, whisk the powdered egg whites and water in a small bowl until foamy. Using a small, clean paintbrush, brush the mixture onto the edible flowers, coating the back first. Do this over a small plate, letting the front of the flower rest on the plate as you're coating.
Sprinkle the superfine sugar over the entire flower, and shake off the excess. Place the flowers on a wire cooling rack to dry. (Or, place the flowers in a food dehydrator set on the lowest setting for a few hours.) They're dry when the flowers are stiff.
Make the sugar cookie bars:
Grease a 9x13 pan. Preheat oven to 375°F.
Whisk together the flour, baking powder and salt. Set aside.
In the bowl of an electric mixer, cream together the butter and sugar until light and fluffy. Add in the eggs, sour cream, zest and extracts, beating until combined. Scrape down the sides and bottom of bowl as needed.
Add the flour mixture in two additions, beating on low just until combined. Spread evenly with an offset spatula in the prepared pan.
Bake for 15 to 18 minutes, or until done. Let cool completely.
Make the strawberry glaze:
Process the strawberries and lemon juice in a blender until smooth. Drain the blended strawberries through a fine sieve, using a rubber spatula to press through. Discard the seeds.
Sift the sugar into a large mixing bowl. Add the strawberry puree and mix on low. Add in the corn syrup and butter, beating until completely incorporated. Add in the vanilla.
Pour two cups of the strawberry glaze over the cooled cookie bars. Let the glaze set up for at least 2 hours. Score the bars using a bench scraper or knife and divide into 24 bars. Place on edible flower on each bar.