Following the directions in the following link, I usually make 3 litres of concentrate, using 3 rounded half-cups of coffee grounds. After brewing for a day and chilling, I'll fill a 16 oz glass about 2/3 full of the concentrate, add a tablespoon of sweetened condensed milk, and top it up with half-and-half cream. Pour into a serving glass or thermos filled with ice cubes. (I don't normally use sugar when I drink hot coffee, just cream, so you may want to adjust the ratios to taste).
I make 3 litres at a time since it's the largest handy jug I have for this purpose, but I'm looking for a bigger one. Basic rule is a rounded half-cup of fine-ground coffee to 1 litre of cold water. To filter the coffee, I just use an old Melita cone filter holder, made to sit on top of a coffee pot, and a #4 cone filter. They clog fast, so you use a few filters.
Best ingredients? I've been doing this for a while. You can't beat Rooster brand sweetened condensed milk, at $1.88 a can, at No Frills. The best coffee for this, hands down, is Kirkland fine-ground dark-roast coffee, about $12-13 for a 1.36 kg can at Costco. Second choice is President's Choice West Coast Dark Roast Gourmet Coffee (fine Grind), about $12 for 875g can at No Frills.
Edit: Don't even think about trying this with Maxwell House or Folgers, it's all crap, and not suitable at all.
Here's the link that let me to this secret ambrosia in the first place:
http://tastykitchen.com/recipes/drinks/ ... ed-coffee/
Enjoy
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