Fill a smaller, decorative OF glass with ice, then stir the remaining ingredients to combine and add to the glass. Garnish.
To make the cordial, first make the oleo-saccharum: in a small glass bowl, muddle the peels of 2 limes and 1 oz Demerara sugar. Chop 2 oz candied pineapple into small pieces and add to the peels and cover. Rest in a warm place for an hour. Add the juice of the limes (about an ounce) and 3 oz pineapple juice and 1/2 tsp citric acid to the peels, muddle the pineapple, wait 5 minutes, then stir to dissolve the sugar and strain this into 4 oz warm whole milk. Wait 5 minutes for the milk to curdle, then filter through a damp Chemex filter in the refrigerator overnight. I know this makes a lot, but it doesn't make sense to make less than 8 oz of the cordial and it's good with sparkling water...