Start by washing and chopping your vegetables. Remove the stems from the broccoli, dice the onion, and finely chop the carrots and celery. Gather all your ingredients on the counter. This will make the cooking process smooth and efficient.

In a large pot, heat a tablespoon of olive oil over medium heat. Add the diced onion, carrots, and celery. Sauté these until they soften and the onion turns translucent—about 5-7 minutes. Stir occasionally to avoid browning.

Once the vegetables are ready, add the crushed garlic and sauté for an additional minute. This step enhances the aroma. Then, toss in your shredded rotisserie chicken, stirring to combine everything well.

Now, it’s time to pour in the chicken broth. Make sure to scrape the bottom of the pot to lift any flavorful bits stuck there. Add the bay leaf, dried Italian herbs, and red chili flakes if you’re going for a kick. Bring it all to a gentle boil.

Next, once your pot reaches a boil, add the broccoli. Cook for about 5 minutes, just until the broccoli becomes tender but still vibrantly green. After this, reduce the heat and pour in the whole milk. Stir to combine.

In a separate bowl, mix the cornstarch with cold water to create a slurry. Gradually add this mixture to the soup while stirring continuously to avoid lumps. Allow it to cook for another 5 minutes on low heat until the soup thickens gently.

Add the Dijon mustard, lemon juice, salt, and freshly ground pepper to taste. Stir in the optional Parmesan cheese if you want to take it over the top. Remove the bay leaf before serving.