For once, a picture! I can't take credit for the punch bowl, unfortunately, but I can claim the garnish.
8 cups water
4 lbs sugar (a standard bag of the regular white stuff)
2 lbs frozen blueberries
2 vanilla beans, split
2 tbsp black peppercorns
Rind from 4 medium lemons
16 oz lemon juice
12 mint sprigs
Place the lemon rinds in a non-reactive bowl and pour a couple ounces of sugar over them. Muddle the peels until the sugar begins absorbing the oil and set aside. Combine the water, sugar, vanilla, and peppercorns in a large stock pot over medium heat and bring to a simmer for about 10 minutes. Add the blueberries and lemon peels, including the oil-soaked sugar, and bring back up to a simmer. Turn off the heat, add the mint sprigs, and let stand and cool for 2-4 hours.
Add the lemon juice and adjust to taste; you can easily add a bit more lemon juice, sweetener (honey would be nice here) or vanilla extract if desired. Carefully strain the whole concoction into the storage vessels of your choice - I love my reserved pair of 1.75L Tanqueray bottles, featuring convenient transport handles!
To serve, pour your storage vessel into a large punch bowl over ice, and add an equal volume of cold water. Top off with soda water to taste; a full liter was just about right for 1.75 liters of syrup plus 1.75 liters of water. Yep, that's 4.5 total liters, and that's why you want a large punch bowl. Keep refreshed with plentiful ice and serve next to some chilled white wine for spritzers, a bottle of gin for highballs, a couple of jiggers for measuring, and brief instructions. My personal favorite combination wound up being about 1 oz gin, 3 oz wine, and 5 oz punch.
Optionally, garnish with lemon wheels, speared with mint sprigs for a nice flowery look. I took some pictures of this one which I'll add here later.