Wash potatoes. Pierce potatoes with a fork. Microwave potatoes for 13 minutes on high. As potato cooks, heat oil in a saucepan over medium-high heat. Add onion and garlic; sauté 3 minutes. Add chicken broth. Combine flour and 1/2 cup milk. Add milk and flour mixture to pot. Add in 1 1/2 cups milk at the same time. Bring to a boil, stirring often. Cook for 1 minute. Remove from heat. Stir in sour cream, salt, and pepper. Peel and discard potato skins. Coarsely mash potatoes into soup. Top with cheese, green onions, and bacon.