Using DiskPart you can unhide an EFI partition on a GPT volume:
Diskpart>
list volume
select volume #
detail partition
set id=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
The default GPT ID for a EFI System partition
is c12a7328-f81f-11d2-ba4b-00a0c93ec93b
, converting to a Basic data partition
with the ID ...C7
automatically unhides the partition.
I have had success with this command prior, but I believe it was for MBR (msdos) partition table.
attributes volume clear hidden
Failure to change the partition type before clearing the hidden attribute, results in this diskpart error message:
Virtual Disk Service error:
The object is not found.
You most likely want to set the ID back to EFI when you are done (eg: modifying BCD)
set id=c12a7328-f81f-11d2-ba4b-00a0c93ec93b