Vegetarian Cheddar Broccoli Soup

Ingredients
4 tablespoons unsalted butter
1 medium yellow onion, chopped
½ teaspoon sea salt
Freshly ground black pepper
3 garlic cloves, chopped
¼ cup all-purpose flour
2 cups whole milk or unsweetened almond milk
2 cups vegetable broth
3 cups chopped broccoli florets
1 large carrot, julienned or finely chopped
½ teaspoon Dijon mustard
8 ounces shredded cheddar cheese, about 2 heaping cups
Homemade croutons, for serving, optional
(I added celery, mushrooms, 1 teaspoon smoked paprika, and modified the broth to be 1 cup mushroom stock,1.5 cups vegan chicken stock, and made sure the cheddar was vegetarian)

Instructions
Melt the butter in a large pot or Dutch oven over medium heat. Add the onion, salt, and several grinds of pepper and cook, stirring, for 5 minutes, or until softened. Stir in the garlic and cook for another minute, then sprinkle in the flour and whisk continuously for 1 to 2 minutes, or until the flour turns golden. Slowly pour in the milk, whisking continuously.
Add the broth, broccoli, carrot, (mushroom, celery, and smoked paprika), and mustard and stir to combine. Simmer for 15 to 20 minutes, or until the broccoli is tender.
Gradually add the cheese, stirring after each addition, until all the cheese is melted and the soup is creamy. Season to taste and serve with croutons, if desired.