In a large pot, add the bacon drippings if you so choose, as well as the butter, melt over med-lo heat. Add the onions and sautee until translucent. Add the flour and stir just until combined with the butter,if it seems to thick and pasty, add an extra tbsp or two of butter, do not brown. add the heated liquid a little at a time as it thickens, while stirring constantly. Once all liquid has been added, let it come to a gentle boil, stirring ocassionally. simmer for about 10 mins. Add the sour cream and stir until combined.