Heat the olive oil in a large Dutch oven or soup pot over medium heat.
Add the onion, carrots, and celery. Cook for 6 to 7 minutes, stirring occasionally, until the vegetables start to soften.
Add the garlic and cook for 30 seconds, stirring the whole time.
Add the butternut squash, chicken broth, chicken breasts, thyme, sage, rosemary, salt, and pepper.
Bring the soup to a gentle boil.
Lower the heat to medium-low and partially cover the pot. Simmer for 18 to 20 minutes, until the squash is tender and the chicken reaches 165°F inside.
Transfer the chicken to a cutting board. Shred the chicken using two forks.
Blend the soup with an immersion blender until smooth and creamy.
Return the shredded chicken to the pot.
Stir in the evaporated milk.
Simmer over low heat for 3 to 4 minutes without letting it boil.
Add the Greek yogurt to a small mixing bowl. Slowly whisk 1 cup of the hot soup into the yogurt.
Remove the soup from the heat.
Stir the yogurt mixture into the soup until smooth.
Add the spinach and stir until wilted.
Stir in the parsley before serving.
Notes
Serving Size: 1¾ Cups
Tips and Tricks
Cut the squash into even cubes - Keep the squash cubes close to the same size so they soften at the same rate.Keep the blender head submerged - Hold the immersion blender below the surface of the soup to reduce splashing.Adjust the thickness - After blending, stir in additional chicken broth ¼ cup at a time if the soup is thicker than you prefer.
Storing and Reheating
Refrigerate - Allow the soup to cool before transferring it to an airtight container. Store it in the refrigerator for up to 4 days.Freeze - Freeze the soup in an airtight freezer-safe container for up to 2 months. The dairy may separate slightly after thawing, but stirring or whisking during reheating can help smooth the broth.Reheat on Stovetop - Place the soup in a saucepan and warm it over low heat. Stir often and do not allow it to boil.Reheat in Microwave - Place one serving in a microwave-safe bowl and cover it loosely. Heat in 60-second intervals, stirring after each interval, until warmed through.