Once the marshmallows have rested, turn the pan over and coax the marshmallows from the pan. This is going to take a little spatula work as well as some time.
It is now time to cut the marshmallows into bite sized little squares of joy. Grab a pizza cutter or a knife (a pizza cutter being much better at this job than any knife) and slice the mass into strips. Dust the marshmallow with confectioners sugar every so often to prevent the newly exposed slices of the marshmallow from sticking back together.
Once the marshmallow has been cut into strips, repeat the cuts in the other direction to form squares. Keep on dusting with more sugar and breaking up the squares until you are left with a pile of individual marshmallow squares.