Quick walkthrough of fixing EFI partition on Windows, from Windows recovery terminal.

Quick_EFI_fix.md

diskpart

list disk

Choose disk number that contains the target Windows install.

sel disk [number you chose]

list vol

Choose volume number that contains EFI partition.

sel vol [volume number you want]

assign letter=G:

You may want to use a letter other than G, if G is taken. But usually it's a safe letter to use.

exit

bcdboot C:\Windows /s G: /f UEFI

And that should be about it.

note to self: the sel disk step doesn't seem to actually do anything. diskpart kept showing me partitions that were on other disks. >.>