I start by heating a skillet over medium heat and crumbling in the Italian sausage along with the chopped onion and minced garlic. I cook this mixture until the sausage is no longer pink and the onion turns soft and translucent. Once it's done, I drain off the excess grease so the soup doesn't end up too oily.
Next, I transfer the browned sausage mixture straight into my crock pot. Then I add the carrots, celery, diced tomatoes, tomato sauce, all the dried herbs, the bay leaf, and the chicken broth. I give everything a good stir so the flavors start mingling right from the start.
I set my crock pot to Low for 8 hours or High for 4 hours, then just let it do its thing. This is my favorite part because I can walk away and let the house fill with that amazing Italian herb aroma while I go about my day.
About 20 minutes before I'm ready to eat, I switch the crock pot to High and stir in the orzo pasta. I let it cook uncovered for those final 20 minutes so the pasta softens perfectly without turning mushy or overcooked.
Once the orzo is tender, I fish out the bay leaf and ladle the soup into bowls. I always finish each bowl with a generous sprinkle of freshly shredded Parmesan right before serving, because that's where a lot of the magic happens.