Preheat oven to 325 degrees. Butter an 8-by-3-inch round cake pan, and dust with flour, tapping out excess; set aside. Stir flour, baking powder, cinnamon, salt, and almonds in a medium bowl; set aside.
Cook Armagnac and fruit in a medium saucepan over medium heat, stirring occasionally, until liquid has absorbed, 15 to 18 minutes. Let cool completely. Chop fruit into 1/2-inch pieces; set aside.
Put butter and sugar into the bowl of an electric mixer fitted with paddle attachment; mix on medium speed until pale and fluffy. Mix in zest and ginger. Mix in eggs, 1 at a time. Transfer to a large bowl. Fold in flour-nut mixture with a rubber spatula. Stir in fruit.
Spoon batter into prepared pan. Bake until a cake tester inserted into center comes out with only a few moist crumbs, about 1 hour 40 minutes. If cake browns too quickly during baking, loosely tent with foil. Transfer to a wire rack; let cool.
Trim cake level with a serrated knife. Bring apricot jam and 1/4 cup water to a simmer in a small saucepan over medium-low heat; strain into a small bowl. Lightly brush cake with the jam syrup.
On a work surface lightly dusted with cornstarch, roll 2 pounds fondant to 1/4 inch thick, brushing off excess cornstarch as needed. Drape fondant over rolling pin; center and place on cake. Starting at top, smooth fondant onto cake with your hands. Trim with a pastry wheel.
On a work surface lightly dusted with cornstarch, roll remaining 1/2 pound fondant to a scant 1/4 inch thick. Cut out 4 small, 4 medium, and 4 large snowflakes. Brush underside of each snowflake with a damp pastry brush, and gently press onto cake. Decorate snowflakes with royal icing.
Cake can be stored at room temperature, tightly covered, up to 2 days.