Add the butter to a large saucepan or Dutch oven and melt over medium heat.

Add the diced onion, celery, carrots, and garlic. Saute until soft, about 4-5 minutes.

Pour in the chicken broth, scraping up any browned bits from the bottom of the saucepan with a wooden spoon.

Increase the heat to medium-high and bring the broth to a boil.

Once a boil is reached, pour in the gnocchi and cook for 4 minutes.

Add the cream, milk, salt, dry mustard powder, and pepper. Stir well.

Once the soup returns to a low boil reduce the heat to medium. Simmer for 5-7 minutes, or until the soup thickens ever so slightly.

Sprinkle in the cheddar cheese and stir until it melts. Turn off the heat and remove the saucepan or Dutch oven from the element.

Stir in the spinach (if using); the residual heat of the soup will cause it to wilt.

Finally, sprinkle in the parmesan cheese and stir just until melted.

Taste and adjust the salt and pepper to your liking.