Line a 9x9-inch baking dish with plastic wrap and spray with non-stick cooking spray. Spray another piece of plastic wrap to cover the top, and set aside.
Place ½ cup of water and ½ cup of the strawberry powder in the bowl of a stand mixer fitted with the whisk attachment. Add the gelatin and whisk just to combine. Scrape down the sides of the bowl.
Combine remaining ¼ cup of water, corn syrup, and sugar in a saucepan. Bring the mixture to a boil over medium heat. Boil the mixture hard for 1 minute. (Do not start the timer until the mixture has reached a hard boil.)
With the mixer on low, carefully pour the hot sugar mixture into the gelatin mixture. Gradually increase the mixer speed to high; beat on high for 12 minutes, until the mixture is fluffy and forms stiff peaks. Add in vanilla extract and beat until just combined.
Pour the marshmallow mixture into the prepared baking dish, using a greased spatula to smooth the top. Cover the candy with the piece of prepared plastic wrap, pressing it down lightly to seal the covering to the top of the candy.
Allow the marshmallow candy to rest at room temperature for 8 hours or overnight. Mix together remaining ¼ cup of strawberry powder, cornstarch, and confectioners’ sugar in a shallow dish. Using oiled scissors or an oiled kitchen knife, cut the marshmallow candy into strips, then into 1 inch squares. Alternatively, use an oiled cookie cutter to cut the marshmallows into shapes. Dredge the marshmallows lightly in the cornstarch mixture and store in an airtight container at room temperature for 3-4 weeks.
Notes
If you are unable to find packaged freeze-dried strawberry powder, you can make your own by pulverizing about 3.6 ounces of whole or sliced freeze-dried strawberries in a food processor. Pulse into a fine powder, then sift to remove the seeds.Try using freeze-dried raspberry powder for a raspberry version of these marshmallows!Humidity is the enemy of homemade candy, so make sure to keep your strawberry marshmallows in a cool, dry place away from humidity, and keep them out of the fridge and freezer.