Combine 3/4 cup cold water and two 1/4-ounce packets powdered gelatin in a small bowl. Mix 1/2 cup each confectioners' sugar and cornstarch in a separate bowl. Sprinkle half of the cornstarch mixture in an 8-inch square pan. Cook 1/2 cup corn syrup, 1 1/2 cups granulated sugar, 1/2 cup water and 1/4 teaspoon salt in a saucepan over medium-high heat until 235 degrees on a candy thermometer, 6 to 8 minutes. Combine the syrup, gelatin mixture and the seeds from 2 vanilla beans in a large bowl. Beat with a mixer on medium high until thick and fluffy, about 6 minutes. Scrape into the pan and spread evenly with a buttered spatula. Sprinkle with the remaining cornstarch mixture. Let dry overnight, then slice into squares.