Citrus oils can be used in place of the zests. For both the citrus and the cardamom, start with smaller amounts and then add more to taste after letting the fluff beat for a few minutes. Check out my Creamy Peppermint Marshmallows post for more information about making marshmallows.
Whisk together the confectioners' sugar and potato starch. Set aside.
Lightly spray an 8x8 (7 and 9 inch square can be used too--it will just change the thickness of the resulting marshmallows) pan. Wipe out the spray, so that only a thin film remains. Set aside.
Place the gelatin in the bottom of a stand mixer bowl. Pour the water and lemon juice over it and leave to soak while preparing the sugar.
Place the sugar, light corn syrup, 1/2 cup water and pinch of salt in a heavy bottomed 2-3 quart sauce pan.
Attach a candy thermometer to the side of the pan and turn the heat onto medium high.
Bring the sugar to a boil and do not stir.
The sugar syrup is ready when the thermometer reaches 242-245 F.
With the stand mixer on the lowest speed, slowly pour the boiling sugar into the stand mixer bowl. Be very careful to not let any of it touch your skin.
Slowly increase the speed of the mixer until you are at medium high. Beat for 5 minutes.
Reduce the speed to medium low and add the zests, vanilla and cardamom.
Increase the speed to high and beat for 9 more minutes. About 2-3 minutes into this, take a good sniff--if the cardamom is not strong enough, add a little more (mine was older and I ended up adding a total of 2 teaspoons). You can also add more citrus zests at this point if you want.
If it is particularly humid, you may need to beat an additional 2-3 minutes. The fluff should be opaque and greatly increased in volume.
Place a large spatula into a bowl of the dredging mix.
Working quickly, lower the bowl while the mixer whips--this will help remove fluff from the whip attachment. Use the dredged spatula to quickly scrape the fluff into the prepared pan.
Let the marshmallow cake set uncovered at room temperature for at least 6 hours--maybe longer if it is humid. I always let mine set overnight because it is more convenient.
When you are ready to slice the marshmallows, dredge a large chef's knife in the dredging mix. Slice and roll each marshmallow in the dredging mixture.