1. Line an 8-in. square pan with foil and lightly grease the foil with 2 teaspoons butter; set aside.
2. In a small saucepan, combine gelatin and water. Cook and stir over medium-low heat until gelatin is dissolved. Add sugar and corn syrup; cook and stir until sugar is dissolved (do not boil).
3. Transfer to a large bowl. Chill until slightly thickened, about 30 minutes. Beat on high speed until mixture is thick and the volume is doubled, about 10 minutes. Spread into prepared pan. Cover and refrigerate for 6 hours or overnight.
4. Using foil, lift marshmallows out of pan. Cut into 1-1/4-in. squares or cut into shapes with cutters lightly coated with cooking spray. Roll in garnishes as desired. Store in an airtight container in a cool dry place. Yield: about 3 dozen.