Prepare a 8x8 pan with parchment paper. Make the paper long enough to hang over two sides so that you can easily remove the marshmallows. Lightly oil the sides of the pan that are not covered by parchment. Dust the bottom of the pan with the powdered sugar and corn starch mixture. Lightly oil a small offset spatula. Set both aside.
In a stand mixing bowl, add the gelatin and ½ cup cold water. Stir to combine. Attach the whisk to get it ready.
In a large pot, add the sugar, agave, molasess and water. Heat over medium until a thermometer reads 240. Do not stir the mixture while it cooks.
Turn the stand mixer on medium low and slowly pour in the sugar syrup. Add the gingerbread spice mix. Turn the mixer to high and whip for 8-9 minutes. The mixing bowl will feel slightly warm, but not hot and will be very fluffy and a pale golden color when its ready. Lift the head of the mixer and whisk up. Watch how the marshmallow flows down into the bowl. If it flows very slowly, its done. If its falls quickly, continue whipping for a minute.
Moving very quickly before it sets, pour the marshmallow into the prepared pan and use the oiled spatula to smooth and even it out. Set aside and let firm for 6-12 hours.
The next day, dust liberally with the powdered sugar and corn starch mixture. Pull up the sides of the parchment paper to remove the marshmallow. Gently pull it away from the bare sides if its sticking. Peel off the parchment sides and cut with a sharp knife into 16 pieces. You can also use a cookie cutter. Dust the knife in the powdered sugar in between cuts to keep it from sticking too much.
Store in an airtight container, liberally coated with powdered sugar and corn starch. They will keep fresh for 3-4 days at room temperature. Do not refrigerate!