Drop sugar cube into a champagne flute. Shake bitters onto sugar and pour in pacharán. Cut a wide strip of orange zest from an orange with a vegetable peeler and twist it to release its oils. Drop into glass, then fill with cava.
*Order pacharan, also spelled patxaran, from winedelight.com. Sloe gin is widely available in liquor stores, but Schick particularly likes the sloe gin from Spirit Works Distillery, in Sebastopol, CA.