   Possible Duplicate:   How do I make my roux taste less like flour?       I'm trying to make a basic cheese sauce for putting over broccoli, etc.  A typical recipe I've tried is:   2 tablespoons butter  2 tablespoons unbleached white flour  1/4 teaspoon dry mustard powder  Sea salt, to taste  1 cup low fat milk  1/2 cups sharp cheddar cheese, grated  White pepper, to taste   Melt butter in a medium saucepan. Whisk in flour, mustard powder and salt to taste. Gradually stir in milk, whisking over med-low heat until thickened. Add cheese, stirring until completely melted. Season to taste with white pepper.  The problem is that it always ends up with a flour/paste undertaste.  Am I just not cooking the Roux sufficiently before adding the cheese or what? 
It seems like you are not cooking the roux. Even a white roux should be cooked. A roux made with butter froths when it is cooked, after that you can add the milk. You can try adding it gradually, if it works for you, I find that dumping it at once and stirring vigorously is better for me - else the first small amount of milk gels the roux into too-hard lumps which the next portion of milk doesn't dissolve. Also, "until thickened" is a bit of a hit-or-miss. I wait until I see bubbles of cooking - not the rapid small bubbles of boiling water, but big, slowly rising bubbles plopping here and there, only then I stop cooking the sauce.  