Line an 8-inch square baking pan with parchment paper.
Combine sugar and vanilla with 1/2 cup water in a non-stick pot over medium heat, stirring to dissolve sugar. Allow mixture to simmer into a syrup, without stirring, until temperature registers 245° C on a candy thermometer.
550 g white sugar, 115 g water
While the syrup is cooking, place tahini, vanilla, and salt in the bowl of a stand mixer fitted with the paddle attachment. Beat on medium speed and carefully stream syrup into the tahini. Mix until syrup is incorporated and the mixture begins to pull away from the sides of the bowl, about 30 seconds to 1 minute. Be careful not to overmix.
300 ml tahini, 1 pinch of salt, seeds of 1 vanilla pod
Transfer the mixture to the prepared pan and flatten it with a spatula; next, place another piece of parchment paper on top and smooth out the halvah with your hands.
Let the halva cool and come to room temperature, then cut into squares.
Store wrapped in plastic, inside a tin box, for a week or so.