Duplicating 'boot sector' for GPT disks in RAID1

[Andrew Wood <andrewjameswood@ymail.com>]

In the past when Ive had 2 disks in a RAID1 mirror Ive been able 
replicated the MBR on both such that the system is capable of booting 
from either in the event of a failure using the command

dpkg-reconfigure grub-pc which then allowed both disks to be selected.

I was under the impression the equivalent for EFI/GPT systems was 
dpkg-reconfigure grub-efi-amd64 however this does not give any option to 
select multiple disks.

How can I ensure that the system is capable of booting from either 
remaining disk in the event of a failure?

Many thanks

Andrew