tarragon, and shallots.
Heat Thickens — and Curdles The
consistency of the hot egg sauces depends on
two factors. One is the form and amount in
which the butter is incorporated. Whole butter
is about 15% water, so each addition thins the
egg phase and the sauce as a whole; clarified
butter is all butterfat, and thickens the sauce
with every addition. The second influence on
consistency is the degree to which the egg
yolks are heated and thickened. The main
trick in making these sauces is to heat the egg
yolks enough to obtain the desired thickness,
but not so much that the yolk proteins
coagulate into little solid curds and the sauce
separates. This happens at around 160–
170ºF/70–77ºC. A double boiler or a saucepan
resting above a larger pan of simmering water
will guarantee a gentle and even heat but will
also slow the cooking; for this reason, some
cooks prefer the riskier but rapid direct heat