How to cook
Combine the lemon juice, sugar and flour in a pot. Heat over medium heat and allow the mixture to boil. Reduce the heat. Gradually pour in half the sauce to the beaten eggs, then return to the pot.
Stir constantly for about 15 minutes. Allow the topping to cool completely, then add the cream. Cool in the refrigerator. Cut the watermelon in half. Carve out the insides of the two halves with a spoon or knife, leaving about 3/4″ (2 cm) of flesh along the rinds of the watermelon.
Cut the insides into coarse chunks. Form something akin to 2 boats. Combine the melon, strawberries, grapes and watermelon pieces. Fill the boats. Serve the dressing separately.