Preheat the oven to 180ºC. Line a 22x24 (approx) baking tray with baking paper or butter/oil to prevent batter from sticking to the pan.
Chop and melt the dark chocolate at bain marie or in the microwave (short 30 sec bursts, mix and repeat). Let it cool down.
Blend the dates, oil, syrup or honey and the eggs in the food processor.
Add the cooled down melted chocolate, the flours, baking powder, salt. Blend a litte more, no need to have a perfectly smooth batter. Pour into the previously lined baking tray.
To make the praliné, blend the hazelnut butter, syrup and water in the food processor until texture is smooth and runny. Add spoonfuls of the praliné on top of the chocolate mixture. Use a fork or toothpick to draw a random patter.
Bake for 25-30 mins. Even if it looks underbaked, it will come together eventually as it cools down. Remove and let it cool down properly before slicing it. Serve with whipped cream, ice-cream or apple compote.