Toast the hazelnuts in a 375 degree oven for 10 to 12 minutes, until fragrant and the skins rubs off easily. Remove as much of the skins as possible by shaking the nuts in a large, covered bowl or by rubbing them with a clean towel.
Add the hazelnuts to your food processor or high-speed blender and process until they become creamy. (This could take several minutes. The hazelnuts will start off powdery and eventually begin to break down and release their oils, forming a creamy paste.)
Add the powdered sugar, cocoa powder, salt, and espresso powder, if using. Cut the vanilla bean in half lengthwise and scrape the insides into the blender or food processor, or use vanilla bean paste.
Gradually add the oil with the motor running, scraping down the sides as necessary, and process until the mixture is a smooth spread. The finished product should be glossy and creamy.
Transfer the spread to a clean pint jar and refrigerate until needed.