In a pot, combine raspberries, sugar, and 1/3 cup water. Simmer over medium-low heat until the raspberries break down, approximately 5 minutes.

Strain the raspberry mixture to remove the seeds, then chill the syrup in the refrigerator.

Fill a cocktail shaker with ice. Add the chilled raspberry syrup, brandy, lime juice, egg whites, and bitters.

Cover the shaker and shake vigorously for about 30 seconds.

Pour the mixture evenly into four glasses.

Garnish each glass with skewered raspberries.