Homemade Broccoli Cheese Soup

- 2 Tbsp butter
- 1 cup onion, finely diced (1 medium onion)
- 2 cups carrots, sliced into thin half-rings (2 medium)
- 4 cups chicken broth
- 4 cups broccoli (chopped into small florets & diced stems)
- 1 tsp garlic powder
- 1 tsp Salt, or to taste
- 1/4 tsp black pepper
- 1/4 tsp thyme
- 3 Tbsp flour
- 1/2 cup heavy whipping cream
- 1 tsp dijon mustard
- 4 oz sharp cheddar cheese, shredded on the large holes of a box grater + for garnish
- 2/3 cup parmesan cheese, shredded