Cut the chicken breasts in half lengthwise if you haven't already. They should about 1/2 inch thick. If the chicken is too thick, the outsides will burn before the center is cooked. Season the chicken on both sides with salt and pepper. Heat olive oil in a large dutch oven over medium heat.
1 teaspoon salt, 1/4 teaspoon black pepper, 1 lb chicken breasts, 2 tablespoons olive oil
Once the oil is hot, add the chicken and sear for 4-5 minutes on each side, doing your best not to move it much while it's cooking. It should reach an internal temperature of 160°F when you pull it off the heat. Remove to a cutting board to rest.
Add the white wine to the pot and scrape any brown bits off the bottom to deglaze the pan.
1 cup dry white wine
Add the diced onion and cook, stirring frequently, until it's soft and translucent, 3-4 minutes. Add the garlic and and Italian seasoning and cook for another 1-2 minutes until fragrant.
1 medium yellow onion, 3 cloves garlic, 1 teaspoon Italian seasoning
Add 4 cups of chicken broth, turn the heat up to medium-high and bring the broth to a boil then reduce to medium-low to simmer for 6-8 minutes.
4-5 cups reduced sodium chicken broth
Use two forks to shred the chicken. You can also cut it into bite-sized cubes if you prefer. Add the chicken to the broth with the parmesan cheese, spinach, and heavy cream, stir, and cook to melt the cheese and wilt the spinach.
1/4 cup parmesan cheese, 1 cup heavy cream, 3 cups fresh spinach
In a separate small bowl, combine the corn starch with 1-2 tablespoons of water and mix to dissolve. Add it to the soup and turn the heat up to medium-high to simmer and thicken. Add up to 1 more cup of broth to reach your desired consistency.
2 tablespoons tapioca
Serve warm with more parmesan cheese and crusty bread.