In a large mixing bowl, sprinkle gelatin over 1/2 cup cold lemon juice. Soak 10 minutes.
While it is soaking, combine sugar, corn syrup, 1/4 cup water in a small saucepan. Bring to a boil. Boil hard for 1 minute.
Pour the boiling syrup into gelatin and mix, using an electric mixer, at high speed. Add the salt and beat for about 10 - 12 minutes.
Add the vanilla and lemon zest. Incorporate into mixture.
Wrap a 9x9 inch pan with plastic wrap and coat the wrap with cooking oil. Then lightly oil your hands and a spatula.
Scrape into the pan and spread evenly. (Don't skip the plastic wrap step or the marshmallow mixture will stick and you'll have a very delicious mess!)
After pouring marshmallow mixture into pan, take another piece of plastic wrap lightly oiled on the side which you will be placing on top of the marshmallow mixture and lightly press marshmallow mixture till flat and even into the pan.
Let marshmallows sit up for about 2 hours.
To remove from pan, dredge whole slab with confectioners’ sugar and cut into squares. Each time you cut or slice you will need to keep using the confectioners’ sugar and dredging each piece so they will not stick to each other and your knife.