Add the lemon juice, lemon vodka, hibiscus vodka, raspberry syrup and egg whites to the cocktail shaker.
Shake the mixture without ice, also known as a "dry shake", about 30 times to build up the egg white foam. (See Notes (3)) You can optionally use a milk frother for this step.
Add ice to the cocktail shaker ("wet shake") and shake well, about 15-20 hard shakes.
Using your regular cocktail strainer and a fine mesh strainer together, strain the liquid into your serving glass.
Optionally garnish with a dusting of freeze-dried raspberry powder or a few whole freeze dried raspberries, and serve.
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Notes
There are some hibiscus vodkas available to purchase, but I suggest making your own infusion using vodka and dried hibiscus flowers. See this section for how to make it at home.
Pasteurized egg whites from a carton work perfectly in this recipe. You can also use powdered egg whites, or a fresh egg white if you are comfortable using it without pasteurization.
You can do your shaking in either order -- dry shake first, and then wet shake, or the opposite. I find that the "Reverse Dry Shake", where you shake with ice first, works better if you are shaking with lots of small ice cubes. If you are shaking with one large ice cube, you can do your dry shake first without worrying that the ice will break up your foam too much.