Add the dried apples, brown sugar, cinnamon, ginger, and mace to a large saucepan. Pour in enough water to just cover the fruit. Bring to a boil over high heat. Reduce to low and simmer, stirring often, until the apples are tender and the mixture is very thick, about 1 hour. If it dries out, add a splash of water. If it is soupy, keep simmering until most liquid cooks off. Remove from heat. Mash with a potato masher into a chunky sauce. Stir in the boiled cider. The texture should be similar to apple butter.

Heat the oven to 350°F. Grease and flour five 9" cake pans. If you have fewer pans, bake in batches.

In a large bowl, whisk the flour, granulated sugar, baking soda, baking powder, and salt. Add the sorghum, 1/2 cup buttermilk, shortening, and egg. Beat with an electric mixer on low until smooth and cookie-dough thick. If the dough seems too dry and stiff, mix in the remaining 2 tablespoons buttermilk.

Divide the dough into five equal pieces, about 7 to 7 1/2 ounces each. Wrap each piece so it does not dry out. With lightly floured hands, press one piece evenly into each prepared pan to about 3/8" thick. Prick all over with a fork.

Bake layers until firm to the touch, about 15 minutes. They will not rise much. Remove from the oven and assemble while the layers are still warm.

Turn the first warm layer onto a large cake plate. Spread with one-quarter of the apple filling, about a heaping cup. Repeat with the remaining warm layers, leaving the top layer plain.

Cover the cake tightly with several layers of plastic wrap and then tea towels, or store in an airtight cake carrier. Let it rest at room temperature for at least 5 days. Dust the top with confectioners’ sugar, slice, and serve.