Heat the butter in a heavy-bottomed pot over medium heat until it melts and starts to bubble gently.
Add chopped onion and celery to the pot, sautéing until they become soft and translucent, about 5 minutes. The aroma will be fragrant, and the vegetables will turn a light golden.
Stir in the diced chicken breasts, cooking until they are lightly browned on all sides, approximately 7-9 minutes. You’ll hear a gentle sizzle and see the chicken turn opaque and develop a slight golden crust.
Pour in the chicken broth, bringing the mixture to a gentle simmer. Use a spoon to skim off any foam that rises to the surface, ensuring a clear broth.
Add the heavy cream and stir well to combine. Reduce the heat to low and let everything simmer gently for about 10 minutes, stirring occasionally. The soup will become creamy and slightly thickened with a velvety texture.
While it simmers, zest the lemon and squeeze out the fresh lemon juice using a lemon squeezer. Add the zest and juice to the soup, stirring to brighten the flavors.
Season the soup with salt, pepper, and dried thyme. Taste and adjust the seasonings to your liking, adding more lemon juice or salt if needed.
Let the soup simmer uncovered for another 5 minutes to thicken slightly and develop all the flavors fully. The consistency should be smooth and creamy, with the chicken tender and cooked through.
Give the soup a final taste and adjust the seasoning as needed. Ladle into bowls, garnish with fresh herbs if desired, and serve hot with a zest of lemon on top for an extra bright note.
