Heat the olive oil in a large saucepan over medium heat. Add the diced onion and sauté for about 5 minutes until translucent. Add the minced garlic and continue to cook for another minute, stirring constantly to prevent burning.
Add the chopped zucchini to the saucepan and stir to coat with the onion and garlic mixture. Sauté the zucchini for about 5–7 minutes until it starts to soften.
Pour in the chicken broth, raise the heat to medium-high, and bring to a simmer. Reduce the heat to low, cover the saucepan, and let the mixture cook for 10–15 minutes until the zucchini is tender.
Once the zucchini is tender, remove the saucepan from heat. Use an immersion blender to puree the soup until smooth. Alternatively, you can carefully transfer the soup in batches to a regular blender and blend until smooth, then return it to the saucepan.
Place the saucepan back on low heat. Stir in the heavy cream and the fresh basil leaves. Cook for an additional 5 minutes to allow the flavors to meld, but do not let the soup come to a boil.
Season to taste with salt and pepper. Ladle the soup into bowls and garnish with optional Parmesan cheese for an added touch of flavor. Serve hot and enjoy!
Notes
Store the soup in airtight containers and refrigerate for up to 4 days or freeze for up to 3 months. Thaw thoroughly before reheating gently on the stove.