How to Make It
In a large saucepan, boil the apple cider over high heat, swirling the pan occasionally, until reduced to 1/2 cup, about 15 minutes. Add 1 cup of the granulated sugar and cook over moderately high heat until a dark amber caramel forms, about 5 minutes. Off the heat, swirl in 2 tablespoons of the butter until melted. Add the apples and cook over moderately high heat, stirring occasionally, until the apples are softened and have absorbed a lot of the syrup, about 8 minutes. Pour the apples into a heatproof bowl and let cool.
Preheat the oven to 350° and position a rack in the lower third. Butter and flour a 12-cup bundt pan. Sift the cake flour, cinnamon, nutmeg, mace, salt and baking soda onto a sheet of wax paper. In a large bowl, using an electric mixer, beat the remaining 3 sticks of butter until creamy. Add the remaining 2 cups of granulated sugar and the vanilla and beat at medium-high speed until light and fluffy, about 5 minutes. Add the eggs, 1 at a time, beating well between additions. Add the dry ingredients in 3 batches, alternating with the sour cream; beat just until combined. Stir 1/2 cup of the batter into the apples, then stir the apple mixture into the remaining batter.
Pour the batter into the prepared bundt pan and smooth the top. Bake for about 1 hour and 10 minutes, or until the top is golden and cracked and a skewer inserted in the center comes out with a few moist crumbs attached. Transfer the cake to a rack and let cool for 20 minutes, then turn it out onto the rack to cool completely.
In a medium saucepan, melt the butter. Add the brown sugar and cook over moderate heat, stirring, until thick and smooth. Gradually stir in the heavy cream and bring to a boil. Cook over moderate heat, stirring occasionally, until thick and bubbling, 3 minutes. Let cool completely, then stir in the confectioners' sugar and vanilla.
Set the cake on a plate and drizzle the glaze all over it. Sprinkle with the pecans, cut into wedges and serve.