What is the ERC (European Research Council)? Find more information here:

-ERC website
-Euresearch: the Swiss guide to European research & innovation

Q: Who should sign the Committment of the Host Institution? The form in the annex of the Information for Applicants says ‘legal representative’.

Find out who is the legal representative of your Host Institution. Every university has its own procedure. Contact your Euresearch Regional Office they will help you.