Roast the hazelnuts in the oven at about 180°C. Keep an eye on them and remove from the oven once they start browning. In the meantime, melt the chocolate in a double boiler over a low heat. If you don’t have a double boiler, place the chocolate in a bowl over a pot of boiling water. The chocolate must melt slowly to prevent from becoming lumpy or grainy. While the chocolate is melting, pop your hazelnuts into a food processor (not a blender) and grind them until they have a semi-buttery consistency – similar to chunky peanut butter. Add all the dry ingredients and the melted chocolate to the mixture and blend together until it becomes smooth. This should take about 15 minutes, depending on your food processor. Add a teaspoon or two of the vegetable oil to aid blending. When you’re satisfied with the consistency, allow the mixture to set for about an hour (put it in the fridge if you like) and serve with fresh croissants or eat it on its own! It also makes a beautiful gift if it’s bottled.