I left about a tablespoon of bacon grease after removing the bacon from the pan, then add the onion. Cook the onion for 5 minutes, stirring occasionally. Add the garlic and continue cooking until the onion is soft and lightly browned, about another 5 minutes.
Add the flour and mix well. Cook for 2 minutes. Add the broth and bring to a simmer, stirring often.
Add the milk, chili powder, pepper and mustard. Return the soup to a simmer, stirring occasionally. Cook for 3 minutes.