In a food processor, combine 1 cup fresh raspberries, balsamic vinegar, olive oil, granulated sugar, honey, and salt.
Process for 10 seconds until the mixture is smooth.
Transfer to a container. Use immediately or cover and refrigerate. Shake well before using.
Assemble the Summer Salad:
In a large mixing bowl, combine the strawberries, blueberries, raspberries, blackberries, and granulated sugar (if using).
Drizzle the raspberry vinaigrette over the mixed berries and toss gently to coat evenly. You can use as little or as much as you want or simply serve on the side so everyone can add their own.
Let the fruit stand for 10 minutes to allow flavors to meld.
Just before serving, stir and garnish with chopped fresh mint leaves.
Notes
While berry salad fruits tend to do better in the summer sun on the beach or at a picnic, keeping your salad cool will keep it fresh longer and make it taste better. Here are a few suggestions:
If you're serving fruit salad outdoors, keep it in a cooler filled with ice or ice packs.
Put a serving bowl inside another bowl of ice.
Chill the serving bowl itself before adding the fruit.
Keep the main bowl in the fridge and serve smaller portions, refilling as needed.
See full article for topping and alternative fruit variations.