400g fresh or frozen raspberries (if frozen, thawed)
500g granulated sugar
20g powdered gelatin
60g egg whites
pinch of salt
1/2 cup confectioners sugar
1/2 cup corn starch
You will also need: a candy thermometer
Make a foil sling for your 13 x 9 baking dish and spray lightly with cooking spray.
In a small saucepan over medium heat, cook the raspberries until soft and juicy. Mash them with a fork to help release the juices. Once soft, press the raspberries through a sieve to remove the seeds and reserve the liquid (approximately 1 cup) in a *large* bowl. If the raspberry liquid seems very thin and watery, reduce it over medium low heat until it thickens. Set the mixture aside to cool and start the sugar syrup.
In a small sauce pan over medium heat, cook the sugar with one cup of water. Stir frequently until it comes to a boil and the sugar has dissolved. Then clip on your candy thermometer and maintain a gentle boil without stirring until it reaches 255F.
While waiting on the syrup, sprinkle the powdered gelatin over the cooled raspberry mixture and whisk. When the syrup is getting close, drop the egg whites and salt into the work bowl of your stand mixer and using the whisk attachment, beat them on medium speed until foamy.
Once the syrup comes to temp, pour the syrup into the large bowl with the raspberry and gelatin. It will bubble up, which is why I emphasized a large bowl earlier. Whisk the mixture to dissolve the gelatin then pour into your mixer with the eggs. Beat on medium-high speed for 5-6 minutes, until the mixture has cooled a bit and tripled in volume. Pour the gooey marshmallow mass into your prepared pan, smooth with an offset spatula and allow to stand at room temperature and cure for several hours (I let them set overnight).
Mix the confectioners sugar and corn starch in a small bowl.
Once the marshmallows have cured, remove from the pan with the foil sling to a cutting board dusted with some of the sugar-corn starch mixture. Remove the foil sling from the mass. As you remove the marshmallow from the pan, toss some of the dusting mixture under the sheet to aid in releasing it. Use as much as you need to keep it from sticking to everything. Now you can cut it into cubes or pull out the cookie cutters and cut out shapes from the sheet. Toss the cut marshmallows into a bowl with the dusting mixture and toss to thoroughly coat. Transfer to an air tight container.