Flaky, all-butter golden pastry filled with a delicately spiced sweet filling, baked until crisp and aromatic.
Simmer the sugar, water, and honey to 115C (soft ball stage), then cool for 5 minutes.
Meanwhile, warm the tahini gently in a large bowl and stir in the vanilla.
Stream the hot syrup into the tahini while beating continuously; the mixture will seize and turn grainy and streaky.
Working quickly before it sets, fold in most of the pistachios.
Press the halva firmly into a parchment-lined loaf pan, smoothing the top; cool completely, then chill for 3 hours.
Cut into thin slices with a warm knife and scatter with the remaining pistachios.