Heat oven to 350 degrees. Coat 2 baking sheets with non-stick spray, if using, or line with parchment paper. Set aside.
Cream the sugar, shortening, salt in a mixing bowl. Mix in the corn syrup. Add the eggs one at a time, beating after each. Beat the mixture until light and fluffy.
In a separate bowl, combine the cake flour and baking powder. Add to the egg mixture alternatively with the milk. Add the vanilla and blend well.
For each cookie, place 1/4 cup of batter on a baking sheet. Use a knife or offset spatula to shape each cookie into a 4 to 6 inch circle; do not flatten. Space the cookies two inches apart.
Bake until light brown around the edges, 18-20 minutes. Cool the cookies completely on wire racks. While cookies are cooling, make the frosting. Place the powdered sugar in a large bowl. Gradually add enough of the boiling water, stirring constantly, until the mixture is thick and spreadable.
Remove half the frosting to a double broiler set over, but not touching,simmering water and add the chocolate. Warm the mixture, stirring, until the chocolate is melted and the frosting is smooth. Remove from the heat.
Turn the cookies to frost the bottoms. Using a knife or an offset spatula, coat half of each cookie with chocolate frosting and the other half with white frosting. Repeat until all cookies are done.