Combine raspberry syrup and mint leaves in a julep cup. Muddle gently, then add remaining ingredients. Fill halfway with crushed ice and swizzle to dilute.
Top with crushed ice and garnish with mint bouquet and fresh raspberries.
To make raspberry syrup: combine 16 oz. Washington red raspberry puree, 10 oz. sugar, 4 oz. water and ¼ tsp. Kosher salt in a large pot. Warm over medium heat until sugar is dissolved. Cool and store refrigerated until ready to use.