Preheat the oven to gas mark 4/180°C/160°C. Grease an 8-inch square pan and line it with two pieces of foil (one across and one along). Brush the foil with some butter.  In a small pan, melt the butter over medium heat. Once melted, remove from the heat, and add the chopped dark chocolate and the cocoa powder. Mix well.  In a large mixing bowl, whisk the eggs, tahini, sugar, carob syrup (or 2 tbsp more sugar), vanilla essence, almond essence, cinnamon, aniseed, cardamom, thyme, orange-blossom water, citrus zests, and salt. Stir in the ground almonds into the moist ingredients. Stir in the melted chocolate mixture into the batter and stir well until very well combined. Pour this batter into the foil-lined dish and spread evenly.  Place the dish in the middle shelf of the oven and bake for 30 minutes or until the edges are set but still looking moist. Cool for another 30 minutes in the dish and remove from the pan by lifting the foil edges. Cool them for an additional hour (very important) and then slice them into equal slabs. Drizzle some honey on top and crushed hazelnuts and pistachios.