How to specify EFI System Partition's mount point in ubu installer?

[PGNet Dev]

Once the aforementioned install to UEFI is complete, without apparent 
error during the install, on guest reboot the client fails to boot, 
dropping instead to UEFI shell:  https://snag.gy/tK9WXR.jpg

Ubuntu-server's grub seems immediately suspect; perhaps too old, not yet 
with full EFI support?

A bit confusing as the Ubuntu installer is clearly EFI-aware.

Whether it works is a question ...