How to Make It
Remove rind from orange using a vegetable peeler, avoiding white pith. Place rind and sugar in a medium bowl; pound rind and sugar together using a muddler or wooden spoon until rind releases its oils. Cover and let stand at room temperature 2 to 4 hours.
Add hot water to rind mixture, stirring to dissolve sugar. Strain through a sieve into a pitcher; discard rind. Stir in sherry and juice; gently stir in cava.