Heat honey on medium heat until your candy or instant-read thermometer reads 115°C, or indicates the “soft ball” stage of candy making.
To confirm that you are at the “soft ball” stage, drop a bit of the honey into a cup of cold water. It should form a sticky and soft ball that flattens when removed from the water.
Have the Tahini ready to heat in a separate small pot, and once the honey is at the appropriate temperature, set the honey aside and heat tahini to 49˚C
Add the warmed Tahini to the honey and mix with a wooden spoon to combine. At first it will look separated but after a few minutes, the mixture will come together smoothly.
Add the nuts, if using. Continue to mix until the mixture starts to stiffen, for a good 6-8 minutes. Pour mixture into a well-greased loaf pan, or into a greased cake pan with a removable bottom.
Let cool to room temperature and wrap tightly with plastic wrap. Leave in the refrigerator for up to 36 hours. This will allow the sugar crystals to form, which will give the halvah its distinctive texture.
Invert to remove from pan and cut into pieces with a sharp knife. Will keep for months in the refrigerator, tightly wrapped in plastic.