Watermelon Sundae

1 (15-oz):cold container whole-milk ricotta (1-2/3 cups) or 1-2/3 cups fresh ricotta
3 oz cream:cheese, softened
1 cup:cold whole milk
1 cup:sugar
2 tablespoons:dark rum
1 teaspoon:finely grated fresh lemon zest
1/2 teaspoon:vanilla
1/8 teaspoon:salt
1/3 cup:cold heavy cream
1 (4 1/2- to 5-lb):wedge of watermelon, cut into 1-inch-thick slices and chilled
1 oz fine-quality:bittersweet chocolate (from a 3-oz bar), shaved (1/4 cup)

Blend cheeses, milk, sugar, rum, zest, vanilla, and salt in a blender until smooth, about 1 minute.
Add cream and blend until just combined, about 5 seconds.
Freeze mixture in ice cream maker, then transfer to an airtight container and put in freezer to harden, at least 3 hours.
Put scoops of ice cream on watermelon slices and top with chocolate shavings.

I found this recipe in Gourmet Magazine in 2006 and LOVE it. You do need an ice cream maker for this one.