Combine the egg whites, sugar, and cream of tartar in the bowl of a mixer. Add the whisk attachment and mix on medium high speed until stiff peaks form. This should only take a few minutes, and you'll want to be careful not to over mix.
Add 2 oz of grapefruit juice, 1 oz tonic, and 1 shot of mezcal to each cup.
Transfer the meringue to a piping bag and carefully pipe a small swirly mountain onto the top of each drink. Then toast them with a kitchen torch, add a sprig of rosemary to each, and enjoy!