Words to the wise from The Ethicurean:
Ideally, the flour is whisked into the liquid and thickens it, but does not clump. If you see clumps of flour, you have too much flour. A little butter will thin the mixture, but don't overdo it, or you will enter a vicious cycle of butter- and flour-adjustment. I once ended up with three gallons of turkey gravy through just such a mistake, having started with a mere quart of liquid.
