50 gr Butter or margarine
[melt in pot]
1/2 - 1 dl flour
[stir it into the butter]
about 5 dl water (from the potatoes if peeled)
some milk
[stir]
Some gravy browning and ketchup
Salt and pepper and other spice if wanted.
[boil and stir, control viscosity with water or milk if too dark brown]