01 - Combine the lemon juice, lemon zest, sugar, milk, vanilla extract, and ice cubes in a blender. Blend on high speed until completely smooth and frothy, approximately 30-45 seconds.
02 - In a clean, dry mixing bowl, beat the egg white and cream of tartar (if using) with an electric mixer or whisk until soft peaks form. Gradually add the 2 tablespoons of sugar while continuing to beat until glossy, stiff peaks form and the mixture holds its shape.
03 - Pour the blended lemon mixture evenly into two tall glasses, filling about three-quarters full. Carefully spoon or pipe the prepared meringue on top of each drink, creating a fluffy, peaked topping.
04 - Sprinkle additional lemon zest and crushed graham crackers over the meringue topping as desired. For a toasted effect, briefly torch the meringue with a kitchen torch until lightly golden. Serve immediately with a straw and spoon.