Ingredients: Per 4 servings
In a bowl, whisk the egg yolks with 2 tbsp. milk. In another bowl, blend the flour into the remaining milk and add the Fontina. Transfer to a saucepan and cook over medium heat, whisking vigorously with a metal whisk, until the mixture thickens.
Add the egg yolks mixture, reduce the heat to low, and continue to cook, whisking occasionally, for about 10 minutes. Remove from the heat. Add the radicchio to the cheese mixture and season with salt. Evenly distribute the cheese mixture among the the vol-au-vents and serve, garnished with the black truffle, if using.