Place the cold water in a bowl and sprinkle the surface with gelatin powder. Set aside to let bloom.
In a skillet, add the coconut milk, vanilla extract, sugar, and salt. Place on the stove over medium heat and stir to mix together the ingredients. Heat over the stove for about 5 minutes until the milk just begins to steam. Remove from heat and add the gelatin. Stir until all gelatin is dissolved. Transfer the coconut milk mixture to a large measuring cup or pitcher to make it easier to pour.
Remove the chilled tart crust from the fridge. If adding sesame, evenly spread the sesame seeds on the bottom of the crust. Pour a small amount of coconut milk (about 2/3 of a cup) onto the sesame seeds so that they are completely covered. Transfer the tart to the fridge and chill for 20 minutes so that the bottom layer has time to slightly set. If you don't want sesame, you can just skip this step.
Remove the tart from the fridge and prepare to pour in the remaining filling. In one hand, hold a spoon with the rounded side facing up. In your other hand, hold the measuring cup with coconut milk. Hold the spoon over the tart crust and slowly pour the coconut milk over the spoon. The milk should flow over the back of the spoon and onto the tart crust. This technique creates a gentler flow of liquid so you avoid disturbing the crust and creating crumbs in the filling.
Carefully place the tart in the fridge and chill for at least 2.5 hours until set
When the filling is set, carefully de-mold the tart. Top with fresh fruit of your choice. Keep in the fridge until ready to serve.
Cover and store any leftovers in the fridge.