Add the bacon to a large skillet and fry until nearly crisp.
Add the onion and garlic to the skillet with the bacon and cook until onion has softened and garlic is fragrant.
Add the bacon, onion, and garlic to a 6 quart slow cooker with the chicken broth and potatoes. Season with salt and pepper.
Cover and cook on high for 3 hours or until potatoes are fork tender.
Add the flour and milk to a mason jar and close tightly. Shake well to combine. Alternately, whisk the flour and milk together in a small bowl.
Pour flour mixture into the soup and stir to combine. Add the cream, evaporated milk, and grated cheddar to the soup and stir.
Cover and cook on high for 30 more minutes.
Use a potato masher to mash the potatoes to reach the desired thickness for the soup. Taste and add additional salt and pepper, if needed.
Ladle hot soup into bowls and garnish with cheddar, bacon, and green onion, if desired.