In food processor (or with mortar and pestle if you feel like it and have the extra time) process the hazelnuts and salt until the nuts are very finely ground. Add the garlic and process again until it is uniform with the nuts.
Add the sorrel, about ½ cup at a time, when it gets too thick to process, start adding the oil slowly, alternating with the remaining sorrel until all incorporated.
Stir in the lemon zest and grated parmesan and season to taste with salt.
Serve with hot pasta like fettuccine or pappardelle or as a condiment with some grilled or poached fish or chicken.
Another delicious option (or use your leftovers) is as a spread on bruschetta and topped with sliced cherry tomatoes.