Finely grate chocolate. Coarsely chop hazelnuts. In a bowl, beat butter until creamy. Gradually stir in eggs, sugar and gingerbread spice. Alternately sift cocoa and flour over mixture and stir in rum. Finally, stir in grated chocolate and hazelnuts.
Line a shallow rectangular baking dish (about 22 x 28 cm or 8 1/2 x 11 inches) with parchment paper. Pour in batter and smooth top. Bake in a preheated oven at 175°C (gas mark 2-3, fan: 160°C) (approximately 350°F), 35-40 minutes. If browning too quickly, cover with a sheet of parchment paper. Let cool.
Invert brownies onto a work surface. Dust with cocoa and cut into pieces.