In a Dutch oven over medium heat, melt butter. Add yelllow onions and cook, stirring frequently, until soft, about 3 minutes. Add garlic and cook 1 minute more.
1/2 cup unsalted butter, 1 large yellow onion, 1 tablespoon fresh garlic
Whisk in flour and continue to cook, stirring constantly, until flour has absorbed butter and has turned a tan color, about 5-7 minutes.
1/3 cup all-purpose flour
Continuing to whisk, pour in a little bit of the chicken broth and allow the flour to absorb it. Once absorbed, pour in a little bit more chicken broth and repeat the process. Continue until all of the chicken broth has been added.
2 1/2 cup low sodium chicken broth
Stil continuing to whisk, pour in half and half cream and stir until combined.
2 1/2 cup half and half cream
Bring soup to a simmer. While soup heats up, season soup with salt, ground mustard, smoked paprika, and pepper, to taste. Once bubbling, reduce heat and let simmer for 5 minutes.