Add an inch of water to the bottom pan of a double boiler or a small saucepan and heat to a simmer.

Add the top half of the double boiler or use a metal bowl that fits rests in the saucepan with the bottom of the bowl above the level of the water. (Your bowl cannot be touching the water or your eggs will cook too quickly.)

Turn the heat to medium and add the egg yolks, sugar and passion fruit puree to the bowl. Stir constantly until the sugar dissolves and the mixture begins to thicken. (Test it to see if it coats the back of a spoon. When it does, it’s done.)

Remove the bowl from the heat and add the salt and the butter, one cube at a time. Stir each cube until it melts before adding the next.

Stir vigorously for about one minute after the last cube is added.

Let the curd cool to room temperature before transferring to a storage container.

Store in the refrigerator for up to 3 weeks.