In a saucepan over medium-high heat, bring the cream and corn syrup to a boil. Remove from the heat and pour over the chocolate. Let melt for 2 minutes without stirring. Whisk until the ganache is smooth. Cover and refrigerate for about 2 hours, stirring 4 or 5 times, or until the ganache has thickened and is spreadable.
With the rack in the middle position, preheat the oven to 350 °F (180 °C). Butter and line two 8-inch (20 cm) springform pans with parchment paper.
In a bowl, combine the flour, baking powder, spices and salt. Set aside.
In another bowl, cream the butter, brown sugar, molasses and vanilla with an electric mixer until light and fluffy. Add the eggs, one at a time, beating until smooth. At low speed, add the dry ingredients alternating with the buttermilk.
Spread the batter into the prepared pans. Bake for 35 to 40 minutes or until a toothpick inserted in the centre of the cake comes out clean. Let cool for 15 minutes. Unmould and let cool completely on a wire rack.
In a small saucepan over medium heat, bring the maple syrup and ginger to a boil. Remove from the heat and let cool.
In a bowl, beat the butter, icing sugar and vanilla with an electric mixer for about 2 minutes or until light and fluffy. Add the cream, 1 tbsp at a time, beating for 30 seconds between each addition.
Cut the cakes in half horizontally to make four layers. Brush the cut side of each layer with the ginger syrup. Spread the ganache evenly over the surface of three layers. Stack the layers and top with the fourth layer. Keep the top and edges free of ganache.
Frost the entire surface and sides of the cake with the buttercream. Decorate with chocolate houses (see recipe below).
or simply with chocolate shavings.