Sauté the onions: In a large pot, melt the unsalted butter over medium heat. Incorporate the chopped onions and cook them until they become tender and translucent, which should take around 4 to 5 minutes.

Cook the vegetables: Add the shredded carrots and chopped broccoli florets to the pot. Continue cooking for an additional 3 to 4 minutes until the vegetables begin to soften.

Create the roux: Sprinkle the all-purpose flour over the sautéed vegetables. Stir and cook for 1-2 minutes to form a roux, which will thicken the soup.

Add the broth and cream: Slowly pour in the chicken broth, milk, and heavy whipping cream while stirring constantly to avoid lumps. Bring the mixture to a simmer, allowing it to thicken, about 5-7 minutes.

Season the soup: Stir in the kosher salt, black pepper, and a pinch of crushed red pepper flakes (if using).

Simmer until tender: Let the soup simmer for 10-15 minutes until the broccoli is tender and the soup has reached your desired consistency.

Add the cheese: Remove the pot from the heat and gradually stir in the shredded cheddar cheese until melted and smooth.

Serve and enjoy: Ladle the creamy broccoli cheddar soup into bowls and serve warm with a side of crusty bread for dipping, just like Panera!