In a large pot or bowl, stir to combine the sugar, lemon zest, lemon juice and pineapple. Let stand for 30 minutes.
Add the hot water and stir to dissolve the sugar. Add the brandy, rum, absinthe, grenadine, cloves, coriander, nutmeg and bitters. Let stand, covered, for at least 1 hour or up to overnight.
In a medium saucepan, scald the milk, then add to the punch. The milk will curdle when mixed with the lemon juice and alcohol. Let stand for 1 hour.
Strain the punch through a double-cheesecloth or a coffee-filter-lined strainer. Transfer to the refrigerator to chill.
To serve, fill a large bowl with the punch and add the 2 sliced lemons. Fill a small glass with ice, add a mint sprig, then fill with punch. Repeat for the remaining cocktails.
The lemon, pineapple and sugar combines to make a mixture called Oleo-Saccharum which dates back to the 19th century, when it was the go-to ingredient for cocktails. It is a great sweetener and base for other beverages like iced teas or lemonade. This mixture can be made 2 to 3 days ahead and kept refrigerated.