In a food processor, grind the hazelnuts into a paste. Add the oil, sugar, cocoa powder, and vanilla and continue processing. Add the melted chocolate and blend well. Strain the mixture through a fine strainer to remove any large grains of nuts. The mixture will be thin and a little warm. Pour into a jar to let cool and thicken slightly. Keeps 1 month, covered, at room temperature.
In a medium bowl, whisk together the eggs and milk. Whisk in the salt, granulated sugar, and flour. Set aside for 30 minutes, if you have got the time. In a nonstick 8 to 10-inch omelet pan, melt about 1/2 teaspoon butter over medium heat. When it foams, pour or ladle in about 1/8 cup (2 tablespoons) batter. Lift and swirl the pan so the batter coats the bottom. Replace the pan on the burner and cook just until set and the underside is lightly browned. Using a spatula or your fingers, flip the crepe, and cook until the other side is lightly browned. Transfer to a platter. Repeat until the batter is used up.
One by one, spread each crepe with a thin layer of the chocolate hazelnut spread, then some banana slices, and roll up like a cigar or fold into quarters. Place 2 crepes on each of 4 serving plates. Sprinkle with confectioners' sugar and serve.
Notes about the recipe: While in Italy we discovered Nutella, a chocolate hazelnut spread that comes in a jar like peanut butter. We can't get enough of it but also have trouble finding it. So I figured out how to make my own! This recipe makes more hazelnut spread than you need but it keeps and is great to spread on toast, inside croissants or on brioche. I've even caught family members just spreading it on a banana as they peel it down, one schmear per bite.