Heat oven to 400 degrees. Pierce potatoes with
a fork and bake at 400 degrees for 50 minutes
until tender. Allow to cool slightly. Scoop
potato flesh into a bowl and mash.
Meanwhile, cook bacon in a large
nonstick skillet until crisp, about
8 minutes. Remove bacon and crumble;
set aside. Reserve 2 tbsp of bacon fat.
In a large pot, add butter and reserved
bacon fat. Heat over medium heat. Add
onion and cook 3 minutes; sprinkle flour
over onion and cook 1 minute. Gradually
whisk in milk; stir in salt, pepper, nutmeg
and cayenne. Add reserved mashed
potatoes and bring to a simmer. Reduce
heat to medium-low and simmer
10 minutes, stirring occasionally. Stir in
2 cups of the cheese, half the reserved
bacon and half the scallions.
Heat broiler. Divide soup equally among
6 flame-proof onion soup crocks. Sprinkle
remaining cup of cheese over tops of
crocks. Broil 4 inches from heat source
for 3 minutes until cheese melts.
Garnish each with 1 tsp sour cream and
remaining bacon and scallions.