For the gelato base: Make the gelato base of your choice, then strain it into an airtight container. Cool to room temperature, then refrigerate overnight. The gelato base must be very cold before churning: this will produce the smoothest, silkiest texture.
For the blueberry puree: Place the fruits in a large bowl, then add the sugar or your choice and the lemon juice. Mix to coat the fruits thoroughly. Let rest at room temperature for 15 to 30 minutes. If the blueberries you’re using are frozen, let rest for 45 to 60 minutes to give the fruits time to thaw completely.
Transfer the macerated blueberries to a saucepan. Place over medium-high heat and bring to a boil. Lower the heat and simmer until the blueberries have broken down and the syrup has thickened, 8 to 10 minutes. If the blueberries you used were frozen, the simmering time could take up to 15 minutes before excess water evaporates and the mixture thickens. Remove from the heat and let cool to room temperature. Transfer to an airtight container and refrigerate at least 2 hours or overnight.
Transfer the blueberry mixture to a blender and mix until you get a fine puree consistency (you can also use a stick blender to do this). Measure out 2 cups (500 ml) of blueberry puree for the gelato (save the remaining puree, if any, to spoon over the churned gelato as a coulis, or add to a smoothie.)
To churn the blueberry gelato: Whisk the blueberry puree into the cold gelato base. Pour into the bowl of an ice cream maker and churn according to the manufacturer's instructions. Stop the machine when the gelato is icy but still soft.
STORAGE: Transfer the blueberry gelato to an airtight container and freeze until firm, about two hours.Blueberry gelato is at its creamiest and best if enjoyed within 2 weeks. Past that, some ice crystals will inevitably start forming (especially if the gelato is kept in the freezer section of a regular fridge, as opposed to a chest freezer) and the texture won't be quite as smooth. The gelato will still be perfectly edible for up to 2 months, but my advice is: enjoy it as quickly as possible after churning.
SERVING: Always take blueberry gelato out to room temperature 20 minutes before serving to make it easier to scoop. This will also allow you to enjoy the treat at its ideal temperature and texture.
MAKE IT DAIRY FREE: When making the gelato base, substitute lactose-free milk or oat milk for the regular milk, and lactose-free heavy cream or soy cream for the regular heavy cream.