Combine the sugar, corn syrup, salt, and 1/2 cup water in a small saucepan over medium heat. Cook until the syrup reaches 240F, about 10-12 mins.
Meanwhile, combine the gelatin with 1/2 cup cold water in the bowl of an electric mixer. Stir gently with a fork until just combined, and let sit undisturbed 3-5 minutes to bloom.
When the gelatin has bloomed, (it will be thick and will have expanded some), run the electric mixer with the whisk attachment at low speed. While the mixer runs, slowly pour the warm syrup into the gelatin.
When all the syrup has been added, increase the mixer's speed a little at a time until the highest speed setting is reached. Whip on the highest speed until very thick, about 8-10 minutes (I recommend setting a timer-- 8-10 minutes is longer than you think!)
Add the cinnamon and vanilla bean scrapings to the bowl and run the mixer until incorporated well.
Line a non-metal 8 x 8 dish (or equivalent) with parchment paper so that it covers the sides and bottom of the dish with 1-2” hanging over the sides (this will make for easy removal of the marshmallow later.) Dust the parchment well all over with powdered sugar through a sieve.
Pour the marshmallow into the dish and dust with more sifted powdered sugar. Drape a piece of cling wrap over the top and allow to set at room temperature overnight.
Once set, turn the marshmallow out onto a clean cutting surface dusted with powdered sugar. Cut into 25 squares, (I cut my 8 x 8 marshmallow 5 times lengthwise and 5 times widthwise), and coat each piece with more powdered sugar to keep them from sticking to each other. Store at room temperature in an airtight container for up to two weeks.