Ina small bowl, sprinkle the gelatin over the water to bloom it.
In a medium sauce pot, add the lemon juice, zest, eggs, butter, and sugar and whisk to combine.
Cook over medium low heat, stirring constantly with a rubber spatula.
The lemon curd mixture will start to thicken and coat the back of a spoon.
It should read at least 160F on an instant read thermometer, then remove it from the heat.
Add in the bloomed gelatin and Smoked Simple Syrup or vanilla and stir until the gelatin has melted.
If there are any egg white bits, you can pass the curd through a strainer before poring into the prepared tart crust.
Allow to cool at room temperature before refrigerating for at least two hours before topping with the meringue.