Preheat the oven to 350 degrees F.
Beat the butter with the whole eggs and the sugar until foamy. Grate the chocolate very finely and add it with the flour, baking powder, cinnamon, rum, and cloves. Fold in the almonds. You might want to use a very sturdy wooden spoon, as the dough gets very thick.
Spread the dough about 1/4-inch thick on a greased baking sheet. Dipping the blade in water helps spread it evenly. Beat the egg white and brush it over the dough.
Bake for 20 to 25 minutes, or until a toothpick comes out clean. Carefully move the entire uncut block to a large cake rack. When it is slightly cool, return it to the baking sheet.
Mix the superfine sugar with 3 tablespoons water in a small saucepan. Simmer until the sugar is completely dissolved. Spread the frosting on the uncut block while still warm and immediately cut it into 1 1/2-inch x 3-inch bars. Leave the bars together until entirely cool and the frosting is set. Store in an airtight container with parchment paper between each layer. They keep for up to 4 weeks.