Process 1 peach in a a blender or a food processor, strain through a fine sieve and measure out 2 oz of the strained peach puree.
Add the elderflower cordial to the strained peach purée. Divide evenly between two chilled champagne flutes and top with chilled Prosecco. Gently stir with a bar spoon to distribute the peach purée.
Notes
Be careful not to stir the cocktail too vigorously as this will release the bubbles and result in a less fizzy drink.