How to Make It
In a skillet, toast the hazelnuts over moderate heat, shaking the pan, until fragrant, 5 minutes. Transfer the nuts to a clean towel and rub off the skins. Coarsely chop 1/4 cup of the hazelnuts; finely grind the remaining 2 tablespoons of hazelnuts.
In a medium bowl, whisk the lemon juice with the 1/4 cup of olive oil, the cheese and the 2 tablespoons of finely ground hazelnuts. Season the dressing with salt and pepper.
Light a grill. Brush the radicchio halves with oil and season with salt and pepper. Grill over moderately high heat, turning, until the edges are lightly charred, 4 minutes. Transfer to a platter and let cool slightly. Spoon the dressing on top, sprinkle with the chopped hazelnuts and serve.