Preheat the oven to 350°. Spread the hazelnuts in a pie plate and toast for about 13 minutes, or until the skins blister and the nuts are golden. Transfer to a kitchen towel and let cool. Rub off the skins and chop the nuts.
Put the kale and broccoli stems in a bowl and season with salt. Using your hands, squeeze the vegetables to soften them slightly.
In a medium skillet, heat the olive oil. Add the leeks and cook over moderate heat, stirring, until softened, about 3 minutes. Add the lemon juice and season with salt and pepper. Pour the dressing over the kale and broccoli and let stand for 2 minutes. Toss well to coat. Add the cheese and hazelnuts and season with pepper; toss again. Serve right away.