Subject to Section, to effect a rescission a party to the contract must, promptly upon discovering the facts which entitle him to rescind if he is free from duress, menace, undue influence or disability and is aware of his right to rescind:
When notice of rescission has not otherwise been given or an offer to restore the benefits received under the contract has not otherwise been made, the service of a pleading in an action or proceeding that seeks relief based on rescission shall be deemed to be such notice or offer or both.
Ca. Civ. Code § 1691