Why does my cheese sauce taste like flour/paste? 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.