Spread flour or powdered sugar 2-inches deep in a large flat pan. Push the hard-boiled egg into the flour or powdered sugar to make molds for the marshmallow mixture. Set aside.
Combine gelatin and cold water. Set aside until water is absorbed by gelatin.
In a heavy saucepan, combine sugar, hot water and ½ cup Karo syrup. Cook on medium heat, stirring constantly until 240 degrees registers on the candy thermometer. Cool a few minutes.
Using an electric mixer, beating at high speed, begin adding remaining ½ cup Karo syrup and all the gelatin mixture 1 tablespoon at a time. Continue to beat 7 to 8 minutes longer after all the gelatin has been added. Add vanilla and beat until well blended.
Pour marshmallow mixture into the flour or powdered sugar egg molds. Sprinkle additional flour or powdered sugar lightly over the entire mixture. Cover pan lightly with a cloth and set aside for 6 to 8 hours or overnight.
Melt chocolate according to package directions. You may use different colors of chocolate - pink - green - red- yellow - etc. Take one egg at a time and dust off the excess flour. Dip marshmallow eggs in melted chocolate and place on waxed paper lined tray. Allow them to set until firm. Tops of eggs may be decorated with nuts, sprinkles or icing flowers. Makes 4-8 2-1/4 x 1-inch Easter eggs. Enjoy!