# Pastebin 3VkgXYIb
steev@finn:~$ cat /etc/grub.d/40_custom
#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
menuentry 'UEFI Shell' --class windows --class os $menuentry_id_option 'osprober-efi-1C4F-E88E' {
        insmod part_gpt
        insmod fat
        search --no-floppy --fs-uuid --set=root 1C4F-E88E
        chainloader /EFI/shell/shellaa64.efi
}