Combine blueberries, lime juice and sugar in the bowl of a food processor. Pulse until pureed. Transfer blueberry mixture to a medium saucepan and bring to a boil over medium heat. Cook for 1 minute. Remove from heat and set aside to cool to room temperature.
Pour cooled blueberry mixture through a fine mesh strainer and discard the solids. Cover and refrigerate the blueberry puree until ready to use.
Pour a shallow layer of the superfine sugar onto a small plate slightly larger than the rim of an old fashioned glass. Moisten half of the rim of the glasses with a little water and then invert the glass into sugar, turning it back and fourth until the moistened half of the rim is completely coated in sugar. Carefully fill each glass three-fourths full with ice.
To serve, pour the blueberry puree and pisco into a large cocktail shaker filled two-thirds with ice. Cover and shake vigorously 20 to 25 seconds. Remove the cap and strain into the ice filled glasses. Garnish each glass with a lemon slice and serve immediately.