1. Melt the butter, stir in the flour using a wooden spoon.
2. Cook over a gentle heat for 3 minutes without browning, stirring throughout.
3. Remove from heat and gradually stir in half the milk, stir hard until well blended.
4. Return to heat, cook slowly until sauce thickens, stirring.
5. Gradually add remaining liquid.
6. Bring to boil, season with salt and pepper. Allow to boil for 2-3 minutes, stirring throughput.
7. This is a thick or coating sauce, used for cauliflower cheese, filing flans and baked casserole dishes.