Farro with Green Onion Sauce, Toasted Walnuts and Asparagus

Combine the farro and stock in a large, heavy saucepan over medium heat. Cover and simmer, stirring occasionally, until the farro is tender (about 45 minutes). Meanwhile, heat the olive oil in a skillet over medium high head. Add the onions and sauté for 5 minutes, until the onions start to soften. Stir in a few pinches of salt. Once soft, puree them in a food processor (just a pulse or two ~ you want to maintain a few chunks). When the farro is nearly cooked, stir in the asparagus. Let the pot simmer for another few minutes, until the asparagus is a vibrant green. Some stock will still be visible in the pot, and that is fine. Stir in the lemon zest, walnuts and the 1/2 teaspoon of salt. Add more salt to taste if needed. Ladle into bowls and garnish with a dollop of creme fraiche (if using), a dusting of parmesan, and a hearty spoonful of the onions.