Heat the olive oil in a heavy-bottomed soup pot (or Dutch oven) over medium heat. When the oil is hot and shimmering, add the chicken sausage and cook until very lightly browned, about 4 minutes.
Add the leek and carrots, and cook for 3-4 minutes just until softened. Stir in the garlic and farro, and cook for 1 minute until the garlic is fragrant.
Add the chicken broth (7 cups for a thicker soup, 8 cups for a more brothy soup) and bring it to a boil. Lower to a simmer, and cook for 15-20 minutes until the farro is al dente (aka just tender).
Add the asparagus to the soup and cook for 3-4 minutes until bright green and just tender. Stir in the lemon juice and baby spinach and cook for 1 minute, just until the spinach has wilted. Taste and season with salt and fresh ground pepper.
Ladle the soup into bowls and top with fresh herbs and shaved Parmesan (if using). Serve with extra lemon wedges if you like.