creamy potato soup

ingredients:
2 - 21/2 lbs of potatoes,
1/3 cup of flour,
5 tablespoons of unsalted butter,
3 cloves of minced garlic,
1 diced large onion,
4 cups of chicken broth,
2 cups of whole milk,
2/3 cup of heavy cream,
1 1/2 teaspoon of salt,
1 teaspoon of black pepper,
1/4 teaspoon of chili powder,
2 - 3 tablespoons of sour cream,
shredded cheddar cheese (optional),
dried chives (optional)