In a small bowl, add in the unflavored gelatine and ½ cup of water. Let bloom.
In a large saucepan, add in the sugar, corn syrup, the remaining ½ cup water, and salt. Place over medium heat and let it come up to 240 degrees F.
Add the strawberry jello to the large saucepan and stir to combine.
Add the bloomed gelatin to a stand mixer bowl and slowly begin to pour the hot sugar into the bowl. This will help dissolve the gelatin.
Begin whipping the mixture with the whisk attachment for 8 to 10 minutes until fluffy and stiff.
While the marshmallow mixture is whipping, prepare the pan.
Lightly spray an 8x8 inch square pan with nonstick baking spray.
In a small bowl, combine the powdered sugar and cornstarch. Reserve half of the mixture to dust the top of the marshmallows.
Dust the greased pan with the powdered sugar and cornstarch mixture.
In the last 1 minute of beating, add the strawberry extract and food coloring. Continue to beat.
Pour the marshmallow mixture into the prepared pan.
If you want a red swirl in your marshmallows add an additional 1 to 2 drops of food coloring on either side of the mixture and use a skewer to swirl it around.
Add the remaining powdered sugar/cornstarch mixture on top of the marshmallows. Spread it to cover all of the marshmallows.
Let the marshmallows rest for at least 4 hours to firm up before cutting. Overnight is best.
Using a sharp knife or pizza cutter, cut the marshmallows into 12 pieces. If the marshmallows are sticky, dust the knife with some of the powdered sugar/cornstarch mixture.
Toss the marshmallows in additional powdered sugar so the sides aren’t sticky.