Celery Colle

Combine first 6 ingredients in container of electric blender; process 3 seconds on high.

Turn blender to low speed; uncover and add 1/2 cup oil in a slow, steady stream. Add vinegar and remaining oil; blend until thickened. Add mustard and chopped egg; cover and blend on high speed until smooth. Chill thoroughly. Pour sauce over celery, and stir well.