In a small saucepan, combine the sugar, water and lime juice and heat over medium-low flame, just until the sugar is dissolved. Remove from heat and allow to cool slightly.
In a martini shaker add the raspberries, strawberries and thyme leaves, reserving 2 raspberries for garnish. Use a muddler or wooden spoon handle and crush the fruit and thyme.
Fill shaker 2/3 full with ice, add the gin, and shake vigorously. Strain into 2 glasses and top with tonic water. Garnish with a raspberry and cheers!
Notes
Tips for Storing
This cocktail is best made fresh to order. The berries and thyme lose their brightness once muddled and left to sit.
You can make the lime simple syrup up to 2 weeks ahead and store it in a sealed jar in the refrigerator.
Pre-muddle the berries and thyme up to a few hours ahead and keep the mixture covered in the fridge until you're ready to shake.
If you're batch-making for a party, mix up the muddled berry base and gin ahead of time, then pour over ice and top with tonic water per glass right before serving.
Already-made cocktails do not store well. The carbonation from the tonic water goes flat quickly, so always finish what's in the glass.