Sprinkle liver with salt and pepper and dredge well in flour.
Melt 1/4 cup butter in a skillet over medium heat. Add onions and cook until tender and lightly browned. Sprinkle 2 tablespoons flour over onions and cook, stirring, for 1 minute. Add broth and cook, stirring constantly, until thickened and bubbly. Turm to low to keep warm.
In another skillet, melt 2 tablespoons butter and cook liver until it loses it's pink color and is lightly browned. DO NOT OVERCOOK unless you are making shoes. :)
Add liver to sauce and return to heat and simmer 10 minutes, covered, until sauce is hot.
Remove from heat and transfer liver to a platter. Stir sour cream into sauce and pour over liver. Serve.