How to Make It
Melt butter in a medium saucepan over medium. Add onion and garlic; cook, stirring constantly, until softened, about 2 minutes.
Whisk in flour, whisking constantly 1 minute.
Whisk in broth and milk; bring to a boil over medium-high. Reduce heat to medium-low, and simmer 5 minutes. Stir in salt and pepper. Use immediately, or cool completely and store in sealed containers or jars in refrigerator up to a week.
Cream of Celery: Add 2 tablespoons finely chopped celery to onion and garlic. Stir in 1 tablespoon finely chopped celery leaves along with salt and pepper.
Cream of Mushroom: Sauté 1/2 cup finely chopped mushrooms in 1 tablespoon olive oil over medium-high. Proceed with step 1, and follow recipe as directed.