In blender, blend watermelon, sugar, cornstarch, half-and-half, lemon juice and whipping cream until smooth.

Using ice cream maker, process gelato according to manufacturer's instructions.

To make whipped cream: When crust and curd are completely cooled, in large bowl, whip cream until stiff peaks form.

Gently push cream to one side of bowl and pour in watermelon curd. Using spatula, gently fold cream and watermelon curd together until no streaks are visible.

Pour creamy watermelon mixture over graham cracker crust. Freeze dessert completely, 4-6 hours or overnight.

When ready to serve, loosen sides with small spatula or butter knife. Turn out onto cutting board and use large spatula to flip so graham cracker crust is on bottom. Cut into eight bars and top each with basil leaf.