How to Make It
Preheat the oven to 375° and position racks in the upper and middle thirds. Line 2 large baking sheets with parchment paper. Spread the hazelnuts in a pie plate and toast for about 12 minutes, until the nuts are fragrant and the skins are blistered. Transfer the nuts to a clean kitchen towel and rub vigorously to remove the skins. Let the hazelnuts cool completely. Transfer the hazelnuts to a food processor and finely grind them.
In a large saucepan, combine the milk with the butter, Frangelico, sugar and salt and bring to a simmer over moderate heat. Remove from the heat. Add the flour and 1/4 cup plus 2 tablespoons of the ground hazelnuts and stir with a wooden spoon until a mass forms. Return the saucepan to moderate heat and cook the dough, stirring, for 1 minute. Transfer the dough to a medium bowl and let it cool for 2 minutes. Using an electric mixer, beat in the eggs one at a time, beating well between additions.
Transfer the dough to a pastry bag fitted with a 1/2-inch plain tip. Pipe 1-inch mounds of the dough onto the prepared baking sheets, about 1 inch apart. Brush the tops with the egg wash and sprinkle with the remaining ground hazelnuts. Bake for about 25 minutes, until the profiteroles are puffed and golden; shift the pans from top to bottom and front to back halfway through baking. Poke a hole in the side of each puff to release the steam. Let the puffs cool completely.
In a medium bowl, using an electric mixer, beat the blue cheese with the mascarpone and heavy cream at medium speed until firm and fluffy. Using a serrated knife, split each puff horizontally and remove any doughy centers with a spoon. Fill each puff with 1/2 tablespoon of the blue cheese cream and replace the tops. Transfer to a platter and serve with the grapes.