In a large stockpot, cook bacon until almost done. Add onion and saute until translucent and softened. Add garlic and cook just until fragrant, about 30 seconds. Whisk in flour until a paste forms. Add chicken stock, slowly, whisking to make sure no lumps form. Stir in potatoes; bring to a boil and cook until potatoes are tender, 10 - 15 minutes depending on the size of your potatoes. Stir in form and cook about 5 more minutes, until thickened. Stir in half and half. Divide into bowls and sprinkle with green onions and bacon, if desired.