Make the watermelon curd by combining the watermelon juice, lime juice, honey and salt in a medium, heavy bottomed saucepan. Stir to combine, then add the lightly beaten eggs.
Place the pan over medium heat and cook, adding the cubed butter to the pan, and stir constantly, until the mixture thickens and
coats the back of a wooden spoon. Immediately remove from the heat and carefully pour through a fine mesh sieve. Allow the mixture to cool completely in the refrigerator. While the curd cools, make the crust.
Preheat the oven to 350°F (180°C). Add the graham crackers to a food processor and pulse until rough crumbs form. Add the honey, salt, and melted butter and pulse until the mixture resembles wet sand.
Line an 8 x 8-inch (20 x 20 cm) pan with parchment paper, then press the graham cracker mixture into the bottom of the pan in an even layer. Bake the crust for about 10 minutes or until just beginning to brown. Allow the crust to cool completely.
When the crust and curd are completely cooled, whip the cream in a large bowl until stiff peaks form. Gently push the cream to one side of the bowl and pour in the watermelon curd. Using a spatula, gently fold the cream and watermelon curd together until no streaks are visible.
Pour the creamy watermelon mixture over the graham cracker crust. Place the loaf pan in the freezer and let the dessert freeze completely, 4 to 6 hours or overnight.
When ready to serve, loosen the sides with a small spatula or butter knife. Turn the bars out onto a cutting board and use a large spatula to flip so the graham cracker crust is on the bottom. Cut into 8 bars and top each bar with a basil leaf. Serve immediately.
* To make your own watermelon juice, put 2 cups cubed seedless watermelon in a food processor and pulse until smooth. Pour the puree through a fine mesh sieve, pressing the juice through with a spoon or spatula. This should yield about 1 cup of juice.