To make the strawberry puree, add the strawberries, sweetener, and water to a saucepan.

Cook over a low-medium heat for 10-15 minutes until the fruit has completely broken down and super soft. Use a stick blender (immersion blender) to puree the fruit until smooth.

Strain the puree through a fine-mesh sieve and leave to cool. Prepare up to this step in advance.

When ready to make the cocktails, stir some heavy cream into the strawberry puree. 

Divide the mixture between four champagne flutes, then top up with Prosecco and serve.