1. Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).
2. Spread out nuts on a lined, rimmed baking sheet. Roast, shaking sheet once for even toasting, until deep brown, about 13–15 minutes.
3. Let cool completely. (If nuts have skins, rub them vigorously in a kitchen towel to remove.)
4. Grind hazelnuts and sugar in a food processor along with the oil until a fairly smooth,buttery paste forms, about one minute. Set aside.
5. Place chocolate in a medium-sized metal bowl. Set bowl over a pot of simmering water; stir until chocolate is melted and smooth.
6. Remove from heat; add butter or margarine,and whisk until completely incorporated. Whisk in remaining ingredients, including the hazelnut mixture.
7. Pour into clean glass jars, dividing equally. Let cool. (Paste will thicken and become soft and peanut-buttery as it cools.) Screw on lids. Use as spread for my Chocolate Fleck Cake, or as desired.
The spread may be made up to one month ahead; keep in a cool, dark place or refrigerate. Let stand at room temperature for four hours to soften. It can stand at room temperature for up to four days. If the consistency is still stiff when brought to room temperature, you can microwave for 10 seconds. To use for cake, make sure to spread it while it is at room temperature.