Sauté the vegetables: Heat the olive oil in a wide pot or deep skillet over medium heat. Add the celery, carrots and onion and sauté for about 5 minutes, until they begin to soften. Season lightly with salt and pepper if desired. Add the garlic and cook for about 1 minute.

Add the broth: While the vegetables cook, blend together the 100 grams sourdough discard and 2 cups of the chicken broth until smooth. Pour into the pot, then add the remaining 4 cups chicken broth and the chicken bouillon paste. Add the poultry seasoning, salt and black pepper and bring to a simmer. As the mixture heats, the sourdough discard will begin to thicken the broth.

Cook the chicken: Add the chicken breasts. If they are very large, cut them in half so they cook more quickly and evenly. Cover and simmer until the chicken reaches an internal temperature of 165ºF. Halved chicken breasts may take around 10 minutes; large whole breasts may take closer to 20 minutes.

Make the dumpling dough: While the chicken cooks, whisk together the sourdough discard, milk, melted butter and Greek yogurt. Add the flour, baking powder and salt and mix just until no dry flour remains. Set aside.

Finish the soup: Remove the cooked chicken to a cutting board. Stir the whole milk and heavy cream into the soup and return it to a gentle simmer on low heat. Do not let the soup boil.

Cook the dumplings: Drop teaspoon-sized portions of dumpling dough evenly over the surface of the simmering soup. Continue until all the dough has been added. Cover the pot and cook at a gentle simmer for about 10-15 minutes, or until the dumplings are puffed and cooked through. Avoid lifting the lid while the dumplings cook, since the trapped steam helps them cook evenly.

Add the chicken: Shred the chicken or cut it into bite-sized chunks, then stir it back into the soup. Taste and adjust the salt and pepper as needed. Ladle into bowls and enjoy!