2/3 c  H2O
1 ts Arrowroot
1 tb Dijon mustard
1/4 c  Finely slivered shallots
1/4 c  Sherry vinegar

In a 1- to 1 1/2-quart pan, blend H2O smoothly with arrowroot. Bring
to a boil, stirring. Chill (quickly, by setting pan in ice water) and
add mustard, shallots, and vinegar. Use, or cover and chill up until
next day. Makes about 1 cup.