In a blender, combine the water or milk, date, peanut butter, banana, strawberries, and raspberries. Add a pinch of salt, if using unsalted peanut butter.
Blend until very smooth, stopping to scrape the blender if needed. You can add more liquid if your blender struggles to process the mixture, but added liquid will dilute the flavor slightly, so use as little extra as possible. Serve right away and enjoy!