In a small bowl, combine powdered sugar and cornstarch until well-blended.
Prepare a 9x13 pan by coating it liberally with nonstick cooking spray, and then dusting it lightly with the powdered sugar mixture.
Return excess powdered sugar mixture to the small bowl.
In a large mixing bowl, place 1/2 cup water and the strawberry puree.
Sprinkle the gelatin on top and stir briefly to distribute evenly. Let sit for at least 5 minutes.
Meanwhile, in a large saucepan over medium heat, combine remaining 3/4 cup water, corn syrup, and sugar.
Attach a candy thermometer, and allow the mixture to cook, stirring occasionally, until it reaches 240 degrees (or about 6-7 minutes).
Once it reaches proper temperature, remove it from heat immediately.
Turn the mixer to low, and very slowly and carefully drizzle the hot syrup into the mixer bowl.
After 1-2 minutes on low, gradually increase the speed of the mixer until it is running on high. Whip the mixture for about 10 minutes, or until it is stiff and shiny. If you stop the mixer and life up the beater, the marshmallow will slowly drip back down into the bowl in a thick, shiny stream.
Pour into the prepared pan, and spread evenly, smoothing the top. Allow to sit at room temperature overnight.
On a large sheet of waxed paper or parchment paper, turn out the pan of marshmallow. Liberally sprinkle it with the powdered sugar mixture.
Using a heart-shaped cookie cutter (or any shape!), cut marshmallow pieces as close together as possible.
Still using the parchment paper as a work surface, toss all the cut marshmallows in the powdered sugar mixture to thoroughly coat.
In a medium saucepan over low-medium heat, melt the chocolate and the coconut oil, carefully whisking them together until smooth.
Dip half of each marshmallow into the chocolate, and return it to the parchment paper to allow the chocolate to set up; at least 1 hour.
Store the marshmallows in an airtight container. They'll keep for at least a week! Enjoy!