Choose a pan for your marshmallows to set in. (Choose a shallow pan like a rimmed baking sheet for smaller marshmallows, or a brownie pan for fatter marshmallows like I've made.) When you've chosen your pan, cut two pieces of parchment paper that are about an inch wider than your pan on all sides. Fit one piece of parchment inside your pan and grease lightly with oil or baking spray. Then, grease one side of the other piece of parchment and set aside for later.

In a small bowl, sprinkle the gelatin over half a cup of cold water and stir to combine. Be sure to break up any lumps. Let sit for 10-15 minutes until the gelatin swells and softens.

Meanwhile, in a heavy bottomed saucepan, combine the remaining half cup of water, sugar, and corn syrup. Cook over high heat, stirring constantly until the mixture comes to a boil. Once the mixture begins to boil, stop stirring and continue to cook over high heat, until the mixture reaches 242 F. Remove the mixture from the heat and let cool to 210 F.

While the sugar mixture cools, heat a pot of simmering water fitted with a heat proof bowl (aka a double boiler). Transfer the gelatin to the bowl and stir continuously until the gelatin is completely dissolved and liquid. Remove from heat and stir in the liqueur.

Working quickly, pour the mixture into the parchment lined pan. Dust with sprinkles if you like! Top with the second piece of parchment, with the oiled side facing down. If necessary, use the back of a spoon or a spatula to lightly smooth the surface and spread into an even layer.

Place the pan in the freezer and chill for at least 8 hours or up to 24 hours.

Remove from the freezer and peel off the top sheet of parchment. (Move quickly, as the longer the marshmallow sits, the stickier it will get. It may be sticky to begin with and that's okay. Boss that parchment off of there!) Dust the surface with cornstarch, spreading lightly with your fingers to coat completely.

Turn the pan over onto a clean cutting surface, peel away the parchment, and dust with cornstarch. Then, cut as desired, continuing to dust all exposed surfaces with cornstarch. I also found it helpful to coat my knife in cornstarch! Store your marshmallows in the freezer in an airtight container for up to four months.