Prepare the nuts. Blanche the almonds and ground them in a nut mill. Roast hazelnuts, remove the skin and grind them. Do not use a blender or food processor because the nuts will come out too mushy.
Melt the chocolate in a bain-marie. At the same time place water and sugar in a saucepan and bring to a boil. Add vanilla flavour. Set the melted chocolate aside.
Add the cubed butter into boiling sugar syrup and stir until it melts. Add rum and set aside.
Combine crushed biscuits with both nuts - but set aside 20 g (1/2 cup) of hazelnuts. Make a little well in the middle and pour in the butter syrup. Mix with a spoon until you get a smooth dough.
Divide the dough into equal parts. Use the scale for precision.
Put the rest of the hazelnuts in one part and melted chocolate in the other.
Divide the chocolate dough into 2 parts. To be super precise, 1 part should be twice as big as the other. In other words, weigh the chocolate dough and divide it by 3. Then make 1 part 1/3 and the other 2/3 of the mass.
Coat the cake pan (27x23 cm) very lightly with melted butter. Place the bigger chocolate dough inside and spread it evenly with your fingers. Place a sheet of baking paper on top and smooth the layer by rolling your hand over it. Remove the paper.
Add the light part of the dough. First sprinkle smaller bits of dough evenly across the pan. Smooth it out through the baking paper, then remove it.
Put the smaller chocolate dough last. This may be the trickiest part because this layer is the thinnest. Sprinkle the dough first then smooth it out through the baking paper.
Place the cake in the fridge for a few hours.
Melt the chocolate and oil in a bain-marie. Pour the icing over the cake and wiggle the pan to spread it evenly. Pop it back in the fridge overnight.
Cut bajadere in 2x4 cm size pieces. Use a Stanley knife to for best and most precise results.
You can freeze bajadere for up to 3 months.