Put two large ice spheres in an oversized glass. Gently pour in the gin and Aperol. Add the juniper berries.
Using a paring knife, cut off a strip of orange zest over the glass. Rub the rim of the glass with the zest and put it into the glass. Slowly pour in the tonic water. Finish with a few drops of both orange and Angostura bitters. Garnish with a squeeze of lime and a sprig of rosemary.