Combine 1/2 cup ice water, granulated sugar, salt, and corn syrup in small saucepan. Cover with lid and heat for 3-4 minutes.
Add remaining ice water and gelatin to separate mixing bowl.
Uncover pot and clip on candy thermometer and cook for 7-8 more minutes until it reaches 240℉. Immediately remove from heat.
Use whisk attachment & begin whisking while gradually pouring hot syrup into gelatin mixture on low speed.
Once syrup is added, increase the speed to high and mix for 10-15 minutes.
Add vanilla and cinnamon right before you're finished mixing.
While it’s whipping, mix powdered sugar and cornstarch in a bowl. Coat pan with nonstick spray and starch/sugar mixture.
Once the marshmallow is done, pour into pan & spread out with nonstick spray coated spatula.
Top the marshmallows with remaining sugar/starch mixture to prevent sticking & let set overnight. Cut into desired shapes, and press cut edges into sugar/starch so they are no longer sticky.