In a cocktail shaker, muddle 4 cherries and any juices. Using a torch, burn a brown sugar cube (I buy French La Perruche because they have the best flavor) and torch until the exterior is burnt. Then add to the shaker along with cherry bitters and muddle until the sugar cube is broken into very small pieces or partially dissolved. Add ice, tequila, and mezcal and shake vigorously until cold.