Raspberry and mint syrup:

• Add raspberries, water and sugar to a saucepan and bring to a boil.  
• Let simmer for 20 minutes, uncovered.
• Add mint leaves, turn off heat and let cool to room temperature.
• Remove the mint leaves and strain through a sieve, crushing the raspberry pulp with a spoon to remove the juice.
• Pour in a bottle and keep chilled.

Cocktail: 

• In a shaker filled with ice, add gin, peach liqueur, raspberry-mint syrup and lemon juice.
• Shake vigorously for 10 seconds.
• Double strain through a cocktail strainer and sieve into a chilled Highball glass filled with new ice.
• Top with Prosecco and garnish with a bunch of mint and some raspberries.