Since it doesn’t all seem to be documented in one place, here’s how to install Debian GNU/Linux from a USB key install of a DVD, but using UEFI. This supplements the “Manually Copying Files to the USB Stick” section of the manual.

You will need:

1. A FAT-formatted USB flash drive.
2. An amd64 network install ISO image from www.debian.org/CD/netinst/, or a larger CD or DVD installer image if you already have one.
3. The latest GTK initrd.gz and vmlinuz images from ftp.debian.org.
4. The latest version of Syslinux from www.kernel.org.

Format the flash drive, then create a new directory efi/boot on it. Copy these files:

1. vmlinuz and initrd.gz into efi/boot.
2. From Syslinux, efi64/efi/syslinux.efi, renamed and copied to efi/boot/bootx64.efi.
3. Also from Syslinux, efi64/com32/elflink/ldlinux/ldlinux.e64 copied into efi/boot with the same name.
4. And the ISO image into the root of the flash drive.

Create a new text file efi/boot/syslinux.cfg with these contents:

PROMPT 1
TIMEOUT 2
DEFAULT linux
LABEL linux
 KERNEL vmlinuz
 INITRD initrd.gz
 APPEND vga=788

No other steps are necessary to make the flash drive bootable. Perhaps after disabling Secure Boot, any recent, reasonably compliant PC will boot directly into the Debian installer.