Preheat oven to 350 F (180 C). To make gingerbread cake, sift together flour, baking soda, and salt. Stir in ginger, cinnamon, and cloves. Add brown sugar and mix. Beat in egg and molasses. Add butter and beat in. Pour in hot water and continue beating. Pour into a greased, 20 centimeters cake pan. Bake for 50 minutes, or until cake springs back when touched.
For pumpkin custard, heat cream in a saucepan with sugar and cornstarch. Whisk egg yolks in a separate bowl. Slowly pour cream mixture into eggs, whisking continuously to avoid cooking the eggs. Pour mixture back into the saucepan and put back on the heat. Cook until thick. Take off the heat. Stir in pumpkin, vanilla, cinnamon, and rum. Chill in the fridge until set.
For the whipped cream, beat cream and sugar in a cold bowl until peaks form.
To assemble, cut top off cake and slice bottom part in half horizontally. Using a gingerbread man cookie cutter, cut ten gingerbread men out of the two bottom parts of the cake, reserving all leftovers. Using a piping bag, cover the bottom of the trifle dish with five centimeters of custard. Top with a small layer of whipped cream. Place top of cake over the whipped cream. Line gingerbread men standing up all around the glass of the trifle dish. Add a second layer of custard and whipped cream. Once the trifle dish is full, sprinkle remaining gingerbread cake pieces over the top.