What's the secret to stuffing so much cheesy flavor into a soup that's only 200 calories a serving? A rind from a wedge of Parmesan cheese is the key to adding lots of rich taste while keeping this comfort food on the virtuous side of the spectrum. (Save leftover rinds from grated cheese in the freezer until needed.)
A second sneaky add-in comes from peeled and diced broccoli stems in the broth, giving you tons of fill-you-up fiber without any fat—and cutting down on waste from this nutritious green vegetable. Serve this soup with a crisp and refreshing salad or a hunk of crusty bread for a full meal.
Slice the florets off the heads of broccoli, rinse in a strainer, and set aside.
With a vegetable peeler, remover the tough outer woody layer from the broccoli stems and finely dice the tender green inner stems.
Heat the olive oil in a medium (3-4 quart) stockpot or Dutch oven over medium low heat.
Stir in the broccoli stems and onion and cook, stirring occasionally, for about 5 minutes until the vegetables are translucent and tender.
Stir in the carrot and 1/4 teaspoon salt and cook for 1-2 minutes more until the carrot is softened.
Add the Parmesan rind and vegetable broth. Cover the pot and increase the heat to medium.
Bring to a boil, then uncover and reduce the heat as needed to keep the broth at a simmer. Cook for 30 minutes, then remove the Parmesan rind with tongs or a slotted spoon.
Add the milk and heat until the soup returns to a simmer. Toss the shredded cheese with the cornstarch and mustard powder in a small bowl, then stir into the soup until melted.
Add half the reserved broccoli florets and cook for 5 minutes until tender.
Remove the soup from the heat. Carefully puree the soup with an immersion blender or countertop blender for 10-15 seconds, just until the florets break up.
Return the soup to the pot and bring back to a simmer. Add the remaining broccoli florets and cook for 5 minutes more until tender.
Taste and add pepper and more salt, if desired. Serve immediately.