Acidulate the OJ with the citric acid. Add the juice to the warm milk to curdle it. Add the curdled milk to a damp Chemex filter over a carafe, being sure to get some of it up the sides of the filter. In a small pitcher, combine everything else, and add to the filter. The filtrate should be pale orange and clear. Place the setup in the refrigerator overnight then transfer the cocktail to a labelled jar.
1 oz Orange juice (strained, blood orange is nice)
1 pn Citric acid
1 1⁄2 oz Milk (whole, warm)
4 oz Campari
1 pn Salt