1. Melt butter in a stock pot over medium heat. Add garlic and saute for 30-60 seconds until fragrant.
2. Add flour to pan and whisk to combine. It will be a somewhat crumbly paste. Slowly add milk a little at a time while immediately whisking constantly to eliminate lumps. Whisk until smooth. NOTE: At this point, if you find yourself with lumps- take the time to whisk vigorously, or use an immersion blender to smooth mixture. If all else fails, you could also place the mixture in a blender. Better to use one of these steps than to have a lumpy soup!
3. Add chicken broth. Bring soup just to a low simmer and cook until thickened, stirring often, about 5 minutes. Because of the milk, this mixture can burn on the bottom of the pot if you aren't stirring pretty regularly.
4. Once soup is thickened, turn heat down to medium-low. Cut potatoes in half length-wise and use a spoon to scoop out potato flesh. I like to do this right onto a cutting board so I can lightly smash them up.
5. Add 1 1/2 cups grated cheese to soup, along with salt and pepper and stir until cheese is melted.
6. Remove pan from heat and stir in 3/4 cup sour cream, 1/4 cup green onions, and 4-6 strips of the crumbled bacon. Add additional salt and pepper to taste.
7. Ladle into bowls and top with each serving with extra sour cream, onions, cheese, and bacon.