To make the strawberry puree, wash and hull your strawberries and then blend on low speed until a smooth puree forms.
In the bowl of a stand mixer, combine the gelatin with the strawberry puree and give it a swirl to ensure the gelatin doesn't clump. Let sit.
In a small saucepan, combine sugar, corn syrup, salt, and water. Heat on medium high with the lid on for a few minutes to bring it to a boil. Then, remove the lid and heat on high heat until a candy thermometer reads exactly 240 degrees F. This can take 4-8 minutes. As soon as it reaches temperature, remove it from the heat.*
With the whisk attached to the stand mixer, start mixing the gelatin and puree on low speed. Slowly pour the hot sugar mixture into the bowl. Once all of the hot sugar mixture has been added, turn the speed to high and continue to mix until you get a beautiful pale pink marshmallow mixture that is just warm to the touch, about 13-14 minutes.
While you're mixing the marshmallow, combine corn starch and powdered sugar in a separate bowl. Spray an 8x8 inch baking dish with cooking spray as well as a rubber spatula. You can line your dish with foil ahead of time, if you wish, and then spray the foil. Add about 1/3 of the sugar and corn starch blend, then shake the pan to evenly coat the bottom and sides. Use the spatula to transfer the marshmallow mixture from the bowl to the baking dish and spread into an even layer. Top with half of the remaining sugar and corn starch mixture, and spread it across the top to cover. Allow the marshmallows to sit uncovered 4-10 hours (I let mine sit overnight).
Lift the marshmallows out of the pan and transfer to a cutting board. Cut into desired shapes and then roll each individual marshmallow in remaining sugar and corn starch mixture to coat all sticky sides.
If using freeze dried strawberries, cut a small opening on the top of each marshmallow and press a strawberry piece inside.
Store in air tight container. They can also be frozen, if needed.
* I don't have a candy thermometer (yet), so I used my digital meat thermometer and it worked perfectly.