In a large pot over medium-high heat, melt the butter. Add the onion, carrots, and broccoli, and sauté, stirring occasionally, until they soften, which takes about 3-4 minutes. Add the garlic and cook until it becomes fragrant, around 20 seconds. Stir in the garlic powder, Italian seasoning, kosher salt, black pepper, and crushed red pepper flakes.

Reduce the heat to medium-low and add the flour, whisking until it's fully incorporated and cooked through. Gradually pour in the heavy cream, whisking constantly to prevent lumps. Once the mixture is smooth, whisk in the chicken broth.

Increase the heat and bring the mixture to a gentle simmer, stirring occasionally until the soup thickens, about 5-8 minutes. Add the tortellini and cook until al dente, approximately 5-7 minutes. Remove the pot from the heat.

Stir in the cheese until it melts, then add the cooked chicken. Taste the soup and adjust the seasoning if necessary. Serve the soup in bowls, topped with freshly shaved Parmesan, and enjoy with Dutch oven bread if desired.