Combine gelatin and half the water in a mixer bowl. Set aside and let the gelatin bloom.
Mix sugar, corn syrup, water, and salt in a saucepan. Over medium heat, cook till sugar is dissolved. Turn heat up.
On high heat cook sugar mixture till firm ball stage or till 240 - 250 degrees F. Should form a firm ball when dripped in cold water but still be able to squeeze it. Not rock hard.
Grease 9 x 13 pan with cooking spray.
Using whisk attachment on mixer, slowly add in hot sugar mixture and turn mixer to lower speed.
Increase speed to high and mix until marshmallow liquid is cooled down enough to touch. Mixture should be fluffy. Mix time is about 4 - 8 minutes.
Add in vanilla and mint extract, mint extract is strong so start small and taste. I'd recommend somewhere between 1/8 tsp to 1/4 tsp. (If you are making two toned marshmallows, divide mixture in half and add any extract and flavoring.)
Pour mixture into greased pan. Using a greased spatula, smooth and spread out marshmallows quickly before it starts to set.
Let sit 5 hours or overnight.
Mix confectioners sugar and cornstarch.
Dust top of marshmallows and a cutting board with cornstarch mix.
Flip over pan and let mallow slab fall onto cutting board.
Dust pizza cutter with powder and cut into squares. Or you could use cookie cutter shapes.