Combine 1 cup of whole milk, 3/4 cup of sugar, and 1 cup of heavy cream in a medium saucepan. Heat until it starts to bubble gently, then remove from heat. Add 1 cup of fresh mint leaves, cover, and let steep for 1-2 hours.

Whisk 4 egg yolks in a separate bowl until smooth. Reheat the mint-infused mixture over low heat. Gradually add a spoonful of the warm liquid to the egg yolks while whisking continuously, then pour the tempered yolks back into the saucepan.

Strain the mixture through a fine mesh sieve into a clean bowl, discarding the mint leaves. Stir in 1 cup of heavy cream and a pinch of salt. Cover and refrigerate for at least 4 hours or overnight.

Pour the chilled base into an ice cream maker and churn according to the manufacturer's instructions for about 20-25 minutes. Transfer to an airtight container and freeze for at least 2 hours.

Blend 4 cups of cubed watermelon with 1/4 cup of sugar and 2 tablespoons of lemon juice until smooth. Pour into a shallow freezer-proof dish and freeze for about 30 minutes.

After the initial freeze, use a fork to scrape the frozen mixture every 30 minutes for 3-4 hours until fully frozen. Sprinkle flaked sea salt before serving.

Layer scoopfuls of the ice cream and granita in small dishes or tall glasses to serve. Enjoy the refreshing flavors!