Pre-heat oven to 160°C/325°F. Beat butter and sugar in stand mixer before adding eggs one by one.
In a large bowl, mix chocolate shavings, ground almonds, flour, and cinnamon. Mix the flour mix, along with the rum, into the butter-sugar mix. Transfer to a parchment-lined baking sheet. Bake at 160°C/325°F for approx. 25 min.
While the bars cool, melt chocolate in a heatproof bowl set over a pot filled with simmering water.
Spread melted chocolate over the cooled bars. Sprinkle the chopped nuts on top. Leave to dry for approx. 30 min. and cut into rectangles for serving. Enjoy!