Place bacon in a large, deep skillet. Cook over medium heat until browned. Remove bacon & place onto paper towels, but do not discard bacon grease. Crumble bacon and set aside.
Into a small amount of bacon grease, brown onions & 2 cloves garlic.
In a dutch oven, melt the margarine over medium heat. Whisk in flour until smooth. Gradually stir in milk, whisking constantly until thickened. Stir in potatoes, onions and garlic. Bring to a boil, stirring frequently. Mash slightly with potato masher,if desired.
Reduce heat, and simmer 10 minutes. Mix in 1/2 the bacon, 1 cup shredded cheddar cheese, majority of the sour cream, and spices. Continue cooking, stirring frequently, until cheese is melted.
When serving, sprinkle top with shredded cheddar cheese, bacon bits, scallions & a dollop of sour cream.