The important in preparing béchamel is to avoid lumps. This is my technique. I first melt the butter, than I add slowly by continuously stirring and passing it through a strainer, the flour. Continuing stirring I pour the milk that I made lukewarm before to finish with nutmeg and salt. Bring to boiling slowly and you will notice that the sauce is thickening. Don’t worry if it does not seem thick enough it thickens more while cooling. So it is better to take it away from heat to early rather than overheating and cooking to much as it burns easily, giving a bad taste. Wait five minutes and if for you is not thick enough restart the heating and the stirring.