To make the Isothermal Block I used LED strip's aluminum plate

It perfectly serves the purpose of an Isothermal block which is to thermally couple the cold junctions but isolate them electrically.
Additionally it already has solder pads.

Following are some detailed pictures of the Isothermal block construction:

A small piece is cut out as per requirement:

Made some notches to fit properly:

The plate with holes are to thermally couple the LM35 with the junction plate:

I made a small metal U shaped clamp to fix the TO-92 shaped LM35 with the base plate :

Finally every part is stacked onto a piece of plywood block with screws:

Video contents :

00:00  -  Project Overview
01:31   -   High temperature test demonstration
03:42  -  Medium temperature test
05:30  -  Low temperature test