Melt the butter and allow to cool slightly. Stir in brown sugar and grated Pomelo zest. Add eggs, one by one. Stir.
Mix flour with baking powder and add to the butter and eggs mixture. Mix until smooth.
Peel the pomelo, remove pips and chop in a blender. Add to the butter, eggs and flour mixture. Mix until smooth.
Preheat oven to 180°C. Grease round cake mold, 20-23 cm in diameter. Spread evenly the cake batter in the mold and top it, in turn, with Nutella and marmalade.
Bake the cake for about 35 minutes or until baked through (the trick with a toothpick). After it is done, let it cool, then remove from the mold and serve.