Add the vodka, lemon juice, simple syrup and egg whites to a cocktail shaker. If you want, add 2 dashes of Angostura bitters at this point.
Optionally, add the blender ball into the shaker. You could also use the spring off of a cocktail strainer if you don't have a blender ball.
Seal up the shaker and shake vigorously. This "dry shake" (without ice) will probably take at least a minute to create a strong foam.
Open up the shaker and add in some ice.
Seal it back up, and shake again, about 15-20 good shakes. This "wet shake" will chill and dilute the drink.
Strain the drink into the serving glass. If you have a fine mesh strainer, pour it through both strainers at the same time ("double strain").
Add 5 drops of bitters on top of the foam layer of the drink, dropping them in a circle. Then, use a cocktail pick to drag through the drops, making them look like little hearts.
Add the lemon slice to the rim of the glass, and serve.