Cheddar-Potato Soup

2 teaspoons olive oil
1 cup diced onion
1 cup diced celery
6 cups reduced-sodium chicken or vegetable broth
2 cups mashed potatoes
8 ounces shredded Cheddar
1/2 teaspoon salt
1/4 teaspoon ground white pepper
1 teaspoon dry mustard
Hot sauce, optional

Add oil to a large pot set over medium-high heat. Add onion and celery and saute for 2 to 3 minutes, or until they start to soften. Add stock and mashed potatoes and bring to a simmer.
Using a hand blender or regular blender, puree soup until smooth (when using a regular blender, work in batches to prevent messy cleanups!). Add Cheddar, salt, white pepper, dry mustard and hot sauce. Stir to combine and allow the cheese to melt.