Prepare a square 8x8" or 9x9" baking pan by lining the bottom and sides with parchment paper. Spray with canola oil.
Mix the Tahini thoroughly before measuring. It separates easily and the thicker part at the bottom needs to be mixed in before pouring to measure.
Bring 1 c of water to a boil.
At the same time, start the Tahini on low in a sauce pan. Stir in the vanilla. Continue to heat, while occasionally stirring, until it reaches about 50°C (120°F). Do not heat it up too quickly or go over temp, because it will scorch. Remove from heat when it reaches temperature.
Once the water is boiling, pour it over the sugar in a larger pan and stir until dissolved.
Over high heat, bring the sugar water to a boil until it reaches 121°C (not over 250°F). Use a candy thermometer.
As you're waiting for the sugar water to get to temp, the tahini should reach the proper temperature.
Pour it into the bowl of a stand mixer with the mixing paddle attached.
When the sugar water reaches the proper temp, immediately turn the heat off, and start the stand mixer on low while pouring in the sugar water until combined. Be careful it is scorching hot!
Bump the speed up to 3 and watch carefully as it mixes. It won't take longer than about 30 seconds to get to the proper consistency. When you see the mixture starting to pull away from the side of the bowl, stop mixing immediately, and pour the mixture into your prepared pan.
It will begin to stiffen as you are pouring it into the pan, so be quick about scraping the remains out of the bowl. With a flat scraper or back of a wide wooden spoon, press the mixture into a level layer.
Let cool for about a half an hour at room temp, then remove solidified piece from pan and cut into 36 pieces (6 rows and 6 columns).
Wrap the Halva up in an airtight container or plastic wrap, and keep in fridge. It will last for months as long as it's sealed, but I'm sure it will be long gone by then. Enjoy!