I cut my marshmallows into squares, but you can just as easily use oiled cookie cutters to cut into any shape. You can also use a smaller baking dish, like an 8x8 pan, to make larger squares or pipe the marshmallows into any shape you want. After you're done whipping the marshmallow mixture, transfer it into a piping bag and wait until it becomes set enough to hold its shape before piping it out.