For the Filling:
Puree the watermelon chunks in a blender, then pour it through a wire sieve into a large saucepan. Push on the solids to extract the juice, then discard the solids and thoroughly rinse the sieve. You should have around 4 cups of puree. Measure out 1/4 cup of the watermelon juice with a small measuring jug and set aside. Add the sugar to the watermelon juice in the pan, stir, and bring to a boil, stirring occasionally.While the juice is coming to the boil, add the cornstarch to the reserved juice and whisk until the mixture is completely smooth.
When the juice is boiling, whisk the cornstarch mixture again, then whisk it into the boiling juice. Boil for 4 minutes, whisking constantly and scraping the sides and bottom of the pot. The mixture will begin to thicken. Pour the mixture through the cleaned sieve into a bowl to remove and lumps that might form. Leave the filling to cool for about 20 minutes.
For the Topping
1 cup heavy whipping cream
1/4 cup sugar
Whip the cream until soft peaks form, then drizzle in the sugar and whip until very stiff peaks form. Scoop the cream onto the chilled pie filling and spread it to the edges of the crust, covering all the filling. Chill in the fridge for an hour before serving. The pie will keep in the fridge for a day.
This pie is great right out of the fridge, but I have discovered that serving after it’s been out of the fridge for half an hour or more intensifies the watermelon flavor. But don’t leave it outdoors!
If you have some leftover watermelon, why not make some Watermelon Sweet Tea?