Melt chocolate using double boiler method (the bowl containing chocolate should not touch the water). To a pan add water, invert a bowl and over that bowl keep the bowl containing chocolate. Melt it well and set aside.
To a sauce pan - add hazelnuts roast until crisp and slightly golden. Set aside to cool.
Transfer to a mixer jar, grind it first it will become coarse slowly it will release oil and start to stick the sides of the mixer.
Scrap the sides with a spoon and grind again when its sticky and not too coarse add powdered sugar and salt.
Add coco powder along with oil and vanilla essence.
Grind again so that its well combined.
Keep grinding giving intervals in middle to avoid mixer from getting hot. Once it reaches a gooey consistency (it will not be very cream at this stage) stop grinding. Now take the bowl containing melted chocolate.
Add this mixture to melted chocolate and mix well. Look at the consistency flowing and spreadable.
Store in a clean dry glass jar in room temperature. Homemade Nutella keeps well for at least 10 days in room temperature itself.