Combine graham cracker crumbs with melted butter and salt, and mix by hand to combine. Press into the base of a 9-inch (22-cm) parchment paper lined spring form pan. Refrigerate.
Pour ⅓ cup (79 ml) of cold water into a small bowl. Sprinkle gelatin into the water and set aside for 5 minutes.
Put banana and simple syrup into a small sauce pan over medium heat and cook until banana is cooked through (about 5-8 minutes). Remove from heat and set aside.
Put cream cheese, egg yolk, and sugar into the bowl of a mixer with a paddle attachment (or use a handheld whisk), and beat slowly until mixture is smooth and thick. In a separate bowl, whip cream until thick but not stiff. Set aside.
Stir the soaked gelatin into the warm, but not hot, banana mixture, and stir until gelatin is evenly dispersed. Spoon a little cream cheese mixture into the banana mixture and stir to combine. Then add a little more. This will even out the temperatures of the two resulting in evenly spread gelatin and uncooked egg yolks. Continue until all is added and slowly fold in whipped cream with a spatula until combined.
Pour into prepared pan and chill in the freezer for two hours, or overnight. Assemble toppings just before serving.