Make a simple syrup by combining the sugar with 1 cup of water in a saucepan. Place over medium heat and heat until the sugar is completely dissolved; swirl the pan occasionally. Let cool. You will have about 1 ½ cups of simple syrup.
Once the simple syrup has cooled, place the blueberries in a blender and puree until smooth. Pour through a fine mesh sieve. You should end up with about 1 cup of blueberry puree.
In a large pitcher, combine blueberry puree, simple syrup and lemon juice and mix well.
Add 4-6 cups of cold water. The amount of water you use will depend on your taste, so add as little or as much as you want to achieve your perfect sweet/tart balance. I recommend starting with 4 cups and adding more if desired.
Serve over ice. If desired, garnish with fresh blueberries, fresh mint, and lemon slices.
Notes
Some bits of blueberry skin and pulp may still make it through when straining the puree. If you want to remove the rest, pour the lemonade through a fine mesh sieve before serving. You can either strain the entire batch or strain each glass when serving.You can also make the simple syrup in the microwave by combining the sugar and water in a large microwave-safe measuring cup and microwaving on high for about 4 minutes, stopping halfway through to whisk the mixture.Feel free to use frozen, thawed blueberries. Do NOT drain the blueberries before adding them to the blender.