Dice the celery into 1/4-inch pieces, slice the carrots into 1/4-inch rounds, and mince the onion and garlic cloves—having everything prepped before you start cooking ensures the soup comes together smoothly. While you're prepping, pat the chicken breast cubes dry with paper towels and season them lightly with salt and pepper. Heat the butter and olive oil in a large pot or Dutch oven over medium-high heat until the butter is foaming, then add the chicken cubes in a single layer. Let them sear undisturbed for 2-3 minutes per side until golden brown on the outside (they don't need to be cooked through). Transfer the seared chicken to a plate and set aside—this browning step builds deep flavor into the broth.

In the same pot with the rendered fat, add the diced celery, sliced carrots, and minced onion over medium heat. Sauté for 5-7 minutes, stirring occasionally, until the vegetables soften and the onion becomes translucent. Add the minced garlic and cook for 30 seconds until fragrant, then sprinkle the flour over the vegetables and stir constantly for 1 minute. This creates a light roux that will help thicken the soup and give it a silky mouthfeel.

Pour the chicken broth into the pot, scraping the bottom with a wooden spoon to release any browned bits stuck to the pan—these add incredible depth. Add the Italian seasoning and bay leaf, then return the seared chicken to the pot along with any accumulated juices. Bring the soup to a boil over high heat, then reduce to a gentle simmer, cover partially, and cook for 15 minutes. The chicken will finish cooking through in the simmering broth while the flavors meld together.

Stir the orzo directly into the simmering soup and cook uncovered for 10 minutes, stirring occasionally to prevent sticking. The orzo will absorb some of the flavorful broth as it cooks—I like to give it a stir halfway through to ensure even cooking. The pasta should be tender but still have a slight bite to it when done.

Remove the pot from heat and stir in the lemon juice and fresh parsley. Taste the soup and season with additional salt and pepper to your preference—I always taste before adding salt since the broth already contains some. Remove the bay leaf before serving. The lemon juice adds a bright, fresh note that brings all the flavors into focus without overpowering the delicate chicken and herbs.