Add passion fruit, and ¾ cup sugar to the blender.
Blend until sugar has dissolved.
Add egg yolk and lemon juice to the passion fruit mixture and blend until smooth.
Using a small bowl or ramekin, bloom (or soften) gelatin by pouring the 1 tbsp. of unflavored gelatin into the ¼ c of water. Let sit for 3-5 minutes until softened. Note: do not pour it out in a lump(it will not soften), sprinkle it on top of the water and stir any lumps immediately until well combined.
Transfer passion fruit mixture from the blender to a sauce pot.
Heat on low until small bubbles start forming around the edge of the pot, while continuously stirring the mixture.
Just before the mixture boils take the passion fruit mixture off the heat.
Thoroughly rinse the blender and remove all the excess water on the bottom.
Pour passion fruit mixture in to the clean blender.
Add cold butter in tbs sized chunks, also add salt and the softened gelatin to the blender.
Blend until smooth and glossy.
Allow to cool for 30 min.