To Set the Gelatin:
Pour 1/2 cup of the coffee in the electric mixer bowl. Sprinkle the gelatin and let it sit for 10 minutes.

Combine the granulated sugar, corn syrup, and 1/4 cup of coffee in the saucepan.

Bring to a boil and boil hard for 1 minute.

Add the boiling liquid carefully to the gelatin mixture.
Mix at high speed and add the salt.
Beat for 12 minutes. Add the vanilla and incorporate into the mixture.

You should have a very gooey delicious marshmallow cream at this point.

Lightly oil your pan and spatula and scrape the mixture into the pan.

Spread evenly. Reapply oil lightly as needed.

Cover loosely and let sit at least 4 hours in a cool, dry place.

Spread powdered sugar onto your work surface.
Gently tip the giant marshmallow out of the pan and dust with more powdered sugar.
Use a knife or scissors dipped in powdered sugar to first cut strips and then cubes. You could also try shaped cookie cutters liberally dusted with powdered sugar.
Dredge the marshmallows in powdered sugar.