In a cocktail shaker filled with ice, combine the raspberry-infused gin and the rose syrup. Shake vigorously until well combined. Pour into a champagne flute and top with Brut Rose. Garnish with rose petals and a few raspberries from the gin mixture.
Place the gin and raspberries in a covered glass jar and allow the mixture to infuse for at least 3 days. Store in the refrigerator.