booting by UEFI?

[Eben King <eben@gmx.us>]

I think I've done everything reasonable in my firmware to ensure booting by
EFI.  I have:

Storage boot option control      UEFI only
Other PCI device ROM priority    UEFI only
(other options for both are "Legacy only" and "Disabled")

The boot device is currently /dev/sdb which has a GPT partition table, and
its first few partitions are

number  size   mount point
1       953MB  /boot
2       2GB    /
3       10GB   /usr
11      9GB    /home
13      48GB   swap
5       953MB  unmounted, filesystem="grub2 core.img", flags="bios_grub"

The first four are ext4.

I do recall it was a pain to make d-i keep the GPT table not overwrite it
with an MBR one.

My motherboard is a Gigabyte H170 with 32 GiB RAM and I run Debian 12.8.  I
swear I ran a program that showed me EFI boot vars (if they exist) and it
showed nothing.  But now I can't remember what that program was.  How can I
ensure that I'm actually booted using EFI?