Melt the shortening and butter together in a medium saucepan. Let cool.
Sift the flour, sugar, spices, and salt into the bowl of a standing mixer.
Mix the butter mixture into the flour mixture with the paddle attachment until sandy. Add the corn syrup and vanilla and mix until evenly incorporated, but still crumbly in texture. Press the dough together by hand and divide into 4 equal portions. Press into disks about 1/2-inch thick. wrap in plastic and refrigerate for at least 2 hours or overnight.
Dust the dough and a work surface with flour. Roll the dough about 1/4-inch thick. Cut into desired shapes. Transfer to a parchment lined baking sheet. Refrigerate until firm, about 30 minutes.
Position racks evenly in the oven and preheat to 350 degrees F.
Bake until a rich tawny brown, about 25 to 30 minutes. Cool on a rack.
Combine all the ingredients, except the food coloring, in the bowl of a standing mixer fitted with the paddle attachment. Mix slowly until stiff enough to form peaks. The icing should be pure white and thick, but not fluffy and bubbly. If the frosting is overbeaten, it will get aerated which makes it harder to work with. If this happens, let the icing sit to settle, then use a rubber spatula to vigorously beat and smooth it out.
Alternatively, combine ingredients in a large bowl, and beat with hand beaters on low speed until the frosting thickens to stiff peaks.
Add up to 1 tablespoon food coloring and mix with a rubber spatula until the color is uniform. (Adding too much color reduces the sheen of the frosting and can break down the consistency of the frosting over a couple of days.) Store icing, covered, with plastic film on the surface of the icing.
This recipe made 2 times (separately) is about the right amount to decorate and assemble the entire train. It's a good idea to make a thick version for attaching train parts and a thin one for piping decoration.
From Food Network Kitchens, Copyright 2005 Television Food Network, G.P. All rights reserved.