In a small bowl, combine confectioners' sugar and cornstarch. Coat an 8-inch or 9-inch baking dish in cooking spray and dust the bottom and sides with half of the sugar mixture. Pour out any excess mixture back into the bowl.
In the bowl of a stand mixer fitted with a whisk attachment, combine rosé, 1/4 cup water, and vanilla. Sprinkle the gelatin over the liquid.
In a small saucepan, stir together the sugar, corn syrup, salt, and the remaining ¼ cup of water. Clip on a candy thermometer. Heat the mixture over medium high heat until it reaches 240ºF and then immediately remove it from heat and bring it over to the mixer.
Turn the mixer on low and drizzle the sugar mixture in a slow and steady stream down the side of the bowl. Once the entire mixture is in, gradually increase speed to high and let it mix for 7-10 minutes total, until lukewarm and fluffy. While the mixer is running, grease a rubber spatula and have that standing by the mixer, as well as the prepared pan.
Using your greased spatula, immediately scrape the mixture into your pans and spread it out evenly as best you can with the spatula. Dust the tops with about half of the remaining powdered sugar mixture and then, if needed, you can use your hands to further flatten and even out the mixture. Let set for an hour, cut into squares, and then dust the edges of the squares with the remaining powdered sugar mixture.