Add the blackberries, basil, honey, and water to a small saucepan set over medium heat.

Simmer, stirring occasionally, until the mixture is heated through and starts to thicken approximately 4-5 minutes.

Gently press on blackberries while heating to release juices.

Remove from heat and strain mixture through a fine-mesh strainer to remove solids. Reserve remaining liquid and set aside to cool.

If using, divide the Elderflower liqueur among four champagne flutes, along with a drizzle of the blackberry simple syrup. Finish by topping off each glass with some chilled Prosecco.

Garnish each glass with 2-3 fresh blackberries and a sprig of fresh basil, if desired, before serving.