Prepare lavender syrup: Add sugar, lavender and water to a small saucepan over medium heat. Bring to a boil, stirring occasionally. Reduce heat and simmer for 10 minutes. Remove from heat and let the lavender infuse in the mixture until cooled. Strain the mixture into a jar, discarding solids.
Peel 2 lemons using a vegetable peeler and add to a blender. Juice all the lemons and add to the blender. You should have about 1/2 cup of lemon juice. Add water and condensed milk to the blender and blend until the lemon peel is broken down, about a minute.
Strain the mixture into a pitcher. Add lavender syrup and stir. Divide into glasses over ice. Add 1 1/2 oz of Empress 1908 Indigo Gin to each glass. Garnish with lemon and lavender. Stir before enjoying.