Restore Windows 10 EFI boot entry

Question

I used my computer to install W7 on a HDD (from a laptop, that didn't have a DVD drive) and it worked flawlessly. Except that when I removed that HDD (that I had just plugged there the time of the installation) and rebooted, I wasn't able to boot on my regular HDD. I went in the BIOS and saw that the Windows boot manager entry had disappeared.

I tried repairing it using bootrec but it didn't change anything. I also tried resetting the uefi firmware to factory settings, still nothing.

How can I get the entry back?

Edit: to be more clear, I am not using W7, I just used my computer to install W7 on another hard drive (it wasn't supposed to touch my main HDD) and somehow it managed to remove the UEFI entries of the W10 that was installed on another drive

Solution

Stupid me.

This fixed the problem:

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

I had already tried this some hours ago from a W10 live CD but it didn't work so I thought it wasn't worth trying again. But I tried again this time from a fresh W10 install USB and it worked.