Prepare your simple syrup if you don't have any on hand. Combine equal parts granulated sugar and water in a small saucepan. Heat gently, stirring until the sugar is completely dissolved. Let it cool before using.

If using egg white, pour the Amaretto, lemon juice, simple syrup, optional orange juice, and egg white into your cocktail shaker *without* ice. Seal the shaker and perform a 'dry shake' – shake vigorously for about 15-20 seconds. This helps to emulsify the egg white and create a better foam.

Add a generous amount of ice cubes to the shaker. Seal again and shake vigorously for another 15-20 seconds until the outside of the shaker is well-chilled.

Strain the mixture into a chilled coupe or rocks glass filled with fresh ice (if serving on the rocks). If you performed the dry shake, you can double strain through a fine-mesh sieve for an extra smooth texture.

Garnish your Amaretto Sour with a maraschino cherry and/or a fresh orange slice. Serve immediately and enjoy the perfect sip!