Put the blackberries in a pot with a tablespoon of sugar. Boil for 3 minutes or until the sugar is dissolved and the blackberries have released some juice. Allow to cool.
In a jar, crush the blueberries, thyme and juice lemon to release their juice. Add 2 tablespoons of blackberry mixture
Add the St Germain and bourbon.
Before serving, prepare a lemon infused sugar. For that, combine the lemon zest, sugar and thyme in a shallow plate. Dip the rim of the glasses in some lemon juice and then in sugar.
Fill the glasses with ice and serve the St Germain mixture to ¾ of the glass. Complete with sparkling water and stir gently.