1. Line a 9×13 pan with plastic wrap, and spray it with non-stick spray. Sprinkle powdered sugar over the pan.
2. Pour the strawberry puree (or 1/2 cup water for chocolate) into the bowl of a stand mixer fitted with the whisk attachment, and sprinkle the gelatin over the entire surface. Allow this mixture to sit untouched while preparing the remaining ingredients.
3. In a medium saucepan, stir together the sugar, corn syrup, water and salt. Heat the mixture over medium-high heat, stirring every minute. When the mixture begins to form large bubbles, immediately remove it from heat and pour it over the puree/water and gelatin in the stand mixer, with the mixer running on low. Turn the mixer up to medium-high and allow it to run for 15-20 minutes, or until the marshmallow mixture has become very thick.
   • If making chocolate marshmallows, add the cocoa powder and vanilla extract and whip together until combined.
4. Moving quickly, use a spatula to scrape the mixture into the sprayed pan and smooth it out evenly as best as possible. Allow the marshmallows to sit, untouched and uncovered for 8-12 hours.
5. In a small bowl, combine the powdered sugar and corn starch to create the “dusting powder”. When ready to cut the marshmallows, grab the ends of the plastic wrap to lift the marshmallows out of the pan and flip them onto a large cutting board that has been sprinkled with dusting powder.
6. Using a pizza cutter or large knife dipped into the dusting powder, cut the marshmallows into the size you desire. Frequently dust the cutter/knife to keep it running smoothly. Place the cut marshmallow pieces into the dusting powder, shake off the excess and store. If using a cookie cutter, be sure to keep the cutter dusted to prevent it from gumming up.

Marshmallows will keep in an airtight container for 3-4 weeks.