Prepare the simple syrup. Heat the sugar, water, and dried lavender in a small saucepan over medium heat, just until the sugar melts, about 3-5 minutes. Remove from heat and cover to let steep for 10 minutes. Strain the syrup and let cool.

Brew the tea. Pour the boiling water over the tea bags and let steep for 5 minutes. Remove tea bags, pressing excess liquid from the bags, and let cool.

Purée the lavender simple syrup, earl grey tea, blackberries, and lemon juice in a blender until smooth. Strain the puree to remove any seeds. You should have about 3-3½ cups of puree.

In a large pitcher just before serving, slowly and carefully add the sparkling water to the blackberry puree (it should foam up a lot!).

Place 2-3 scoops of ice cream in each of six large glasses and pour blackberry soda over the top. Add a splash more sparkling water to add a little foam to the top and serve immediately.