Lightly spray an 8x8-inch baking pan with nonstick cooking spray. Wipe the pan with a paper towel to leave a thin, even coating across the bottom.

Add flavored gelatin and boiling water to a mixing bowl. Stir for about 2 minutes, or until the gelatin is completely dissolved.

Add mini marshmallows and microwave for 30 seconds. Stir until the marshmallows are completely dissolved. This can take about another 2 minutes of stirring, so continue mixing until no marshmallow pieces remain.

Gently pour the mixture into the prepared pan. Let stand at room temperature for 30 minutes, then refrigerate for 4 hours or overnight until completely set.

Run a knife around the edges of the pan to loosen the Jello. Carefully remove the entire sheet and place it onto a piece of parchment paper.

Roll the Jello into a log and wrap the parchment paper tightly around the roll. Refrigerate for 1 additional hour. This second chill helps the roll hold its shape once sliced.

Remove the parchment paper and cut the log into 12 rounds. If making more than one color, repeat the recipe separately for each flavor.