Preheat the oven to 180C (350F). Grease a 10-cup bundt or loaf tin and dust with flour
Melt the chocolate over a pot of barely simmering water and set aside to cool.
Whisk the egg whites in a stand mixer until they form stiff peaks and transfer to a bowl.
Fit in the paddle attachment and beat the butter and sugar (no need to clean the stand mixer bowl) until light and flutty.
Beat in the yolks, one at a time.
Add the cooled melted chocolate, treacle and stem ginger syrup and beat until incorportated.
Fold in the flour, ground almonds, bicarbonate of soda, chopped stem ginger and spices.
Add a third of the whisked eggs into the batter and beat to loosen. Fold in the remaining egg whites.
Transfer to prepared tin and level. Tap the tin on the counter.
Bake for 40-45 minutes until firm on top and coming away from sides of the tin. Cool in the tin for 10 minutes and carefully turn out onto a cooling rack.
Melt the chocolate and butter over a pot of barely simmering water. Add the gem ginger syrup and stir until smooth.
Pour the chocolate glaze over the cooled cake and decorate with sprinkles or gingerbread cookies.