MikTeX fails to find a font installed in Windows 10 (for XeLaTeX)

I have problem using some open type fonts in Windows 10 with XeLaTeX in 
MikTeX.
I downloaded a Malayalam language font, "Gayathri" and tried to use it 
in XeLaTeX.
This font is clearly listed in the Font catalogue accessible from 
Control Panel.
The Font catalogue lists its name as "Gayathri Regular".
But when I use them in XeLaTeX with the command
      \newfontfamily{\mal}[Script=Malayalam]{Gayathri Regular}
MikTeX complains it cannot find the font and starts building 'tfm's, 
with the following Error message.

      Package fontspec Error: "Gayathri Regular" cannot be found.

I had the same problem with many other fonts in many other languages 
too.
I guess it must be a  problem related to the way MikTex identifying the 
fonts in the operating system.

Another Malayalam language font "Kartika" that comes with Windows 10 
(when I installed the
Malayalam language add-on in Windows 10) works fine in XelaTeX.  Hence I 
am puzzled.
Any help will be appreciated.


_______________________________________________
Q: How can I leave the mailing list?
A: See https://miktex.org/faq/how-can-i-leave-the-mailing-list