First mount

The first time we mount we have to do a little preparation. For Linux, the ESP is going to be a subdirectory of the /boot directory. So, find or mkdir a suitable mount point; mount the xfs partition; mkdir the boot and efi folders; and mount the ESP:

mkdir /tmp/usb-sda
mount /dev/sda2 /tmp/usb-sda
mkdir -p /tmp/usb-sda/boot/efi
mount /dev/sda1 /tmp/usb-sda/boot/efi

Review

# lsblk -f /dev/sda
NAME   FSTYPE LABEL UUID                                 MOUNTPOINT
sda
├─sda1 vfat         68DA-C96A                            /tmp/usb-sda/boot/efi
└─sda2 xfs          dcdff2d3-fb08-420e-a60a-c5df939b497e /tmp/usb-sda

Subsequent mounts

Thereafter, we need only perform the two mount s in the right order and we're good to go.