Season the chicken breasts with 1 teaspoon salt and 1/2 teaspoon black pepper. Pat them dry with paper towels—drying improves browning. Seasoning early helps the meat develop flavor throughout.

In a large Dutch oven or heavy-bottomed pot, heat the olive oil over medium-high heat until shimmering. Add the chicken breasts and sear 2–3 minutes per side until lightly golden (they don’t need to be fully cooked). Searing caramelizes the proteins and creates fond (brown bits) on the bottom of the pot which adds deep flavor to the broth.

Remove the chicken to a plate and lower heat to medium. Add the butter to the pot. Once melted, add the diced onion, carrot and celery (mirepoix). Sauté 5–7 minutes until the vegetables soften and the onion turns translucent—this builds the aromatic base for the soup.

Stir in the garlic and cook 30 seconds until fragrant. Sprinkle the 2 tablespoons of flour over the vegetables and stir to coat. Cook the flour for 1–2 minutes to remove its raw taste and to create a light roux; this will thicken the broth slightly and give it a satin texture.

Slowly pour in 1 cup of the chicken stock while whisking or stirring vigorously to dissolve the roux into a smooth slurry—this prevents lumps. Then add the remaining 7 cups of stock, the thyme sprigs and bay leaf. Scrape up any browned bits from the bottom of the pot; those are flavor.

Return the seared chicken to the pot. Bring the pot to a gentle simmer, then lower heat so the broth barely bubbles. Simmer, covered, for 12–15 minutes or until the chicken reaches 160–165°F (71–74°C). Simmering gently poaches the chicken evenly and keeps it tender.

Remove the chicken from the pot and transfer to a cutting board. Let it rest 3–4 minutes (carryover heat finishes cooking). Meanwhile, bring the broth back to a boil and add the pasta. Cook the pasta in the broth according to package instructions minus 1 minute (it will finish cooking in the soup and absorb flavor). Cooking the pasta in the broth infuses it with flavor but reduces the need for extra pasta water later.

While the pasta cooks, shred the chicken with two forks or chop into bite-sized pieces. Return the shredded chicken to the pot when the pasta is nearly done. Taste the broth and adjust seasoning with salt and pepper—the pasta and chicken stock can change salt balance.

Stir in the lemon juice and chopped parsley off the heat. Lemon brightens and balances the richness from butter and chicken; parsley adds fresh herbaceousness. Remove the thyme sprigs and bay leaf before serving.

Ladle the soup into warmed bowls and, if desired, finish with a grating of Parmesan, a drizzle of olive oil, and more chopped parsley. Serve immediately—pasta will continue to absorb liquid, so leftovers will be thicker; reserve extra stock if you plan to reheat.