Select four cocktail glasses for serving. On a shallow plate, add the sugar, salt and chile powder, mixing to combine well. Place the egg white on a separate shallow plate. Turn the cocktail glass upside down and wet the rim of the glass evenly with the egg white. Dip the wet rim of the glass in the sugar/salt/chile mixture, and coat well. Allow to air dry for a minute or two while you prepare the margarita.

Carefully peel and rinse the cactus pears (see photos.) In a tall glass, combine the cactus pears and lime juice. Using an immersion blender, blend into a puree. Strain the mixture through a fine mesh strainer to remove all seed and pulp. Discard the pulp.

Load a cocktail shaker with ice, and add the cactus pear juice, orange liqueur, and tequila. Shake for 5-7 seconds, and then pour into the prepared glasses.