Step 1

Line a baking sheet with parchment. Spread watermelon on it and freeze at least 4 hours or overnight.

Step 2

Combine sugar and water in a small saucepan over high heat. Cook, stirring until the sugar is dissolved. Stir in the lemon.

Step 3

Transfer half of the frozen watermelon to food processor fitted with steel blade attachment. Drizzle on half of the hot simple syrup and puree, scraping down sides as necessary. This will take several minutes, and require stirring several times to achieve smooth results. If the mixture is quite icy and not pureeing, drizzle on two tablespoons of water to help get the mixture moving. Transfer to a loaf pan or air-tight container and freeze. Repeat with the remaining frozen watermelon and syrup.

Step 4

Serve immediately or freeze up to 2 weeks.