Melt the butter in a pan. Mix it with the flour. Cook until a slight nutty aroma arises. Do not brown.
2
Immediately afterwards, add the milk, very slowly, and the salt and pepper. Mix briskly until the first sign of boiling.
3
The sauce must be quite thick, very creamy. Therefore, let it boil for a few minutes, but remember that when it is cool the sauce is always a little thicker then when it is hot.