01 - Preheat oven to 350°F.
02 - Combine graham cracker crumbs, melted butter, and sugar in a bowl, mixing until the texture resembles wet sand.
03 - Press the crumb mixture evenly into the bottoms and sides of 6 mini tart pans.
04 - Bake for 8-10 minutes until golden. Allow to cool completely before filling.
05 - Blend watermelon cubes, lime juice, and honey until completely smooth. Strain through a fine-mesh sieve to remove any pulp.
06 - Beat cream cheese until smooth. Incorporate sweetened condensed milk, heavy cream, lemon zest, and lemon juice. Continue beating until the mixture is light and creamy.
07 - Distribute the lemon cream evenly among the cooled tart shells.
08 - Spoon a thin layer of watermelon purée over the lemon cream. Use a skewer to gently swirl for a marbled effect.
09 - Transfer tarts to the freezer and chill for at least 3 hours until completely firm.
10 - Remove from freezer and let stand at room temperature for 10 minutes before serving. Garnish with mint leaves, watermelon balls, and additional lemon zest as desired.