Add the frozen blueberries, sugar, lemon juice, and mint leaves into a small saucepan.

Cook on medium high heat until the blueberries juices have released, and the mixture is simmering. Turn down to medium low and simmer for 10 minutes.

Remove from heat and allow it to cool.

Once the blueberry sauce is cooled, strain the blueberries from the sauce into a bowl. Mash the blueberries to be able to get as much sauce from them.

Store the blueberry syrup in a jar in the fridge for 2-3 weeks.

Add 1 cup of water and sugar to a pot and heat on medium high heat until the sugar dissolves. Remove from heat and allow the simple syrup to cool.

Meanwhile, cut the lemons in half and squeeze the juice into a bowl. Repeat with all the lemons.

Add the cooled simple syrup, lemon juice, and water to a pitcher and mix to combine. Adjust the level of tart you want by adding more lemon juice.

Pour in the desired amount of blueberry sauce to the pitcher and mix to combine.

Add some fresh mint, blueberries, ice and lemon slices to the pitcher and serve.