The Uncarved Block

Here's how to make delicious smooth cold-brew coffee:

1. You need a cafetière (French press for my American friends) and a drip filter (like if you were a hipster making a pourover). A chemex works great for this.
2. Ok, now grind the coffee fine as though you're making espresso (that's not what you'd use for a regular cafetière coffee I know). I use about 68g of coffee for 800ml cafetière. Your mileage may vary, but err on the side of more coffee rather than too little. 1.5 - 2 tablespoons per cup of coffee is I think the rule for this sort of thing.
3. Put the ground coffee in the cafetière and pour on regular cold tap water. You might want to use filtered water if your tap water doesn't taste good enough to drink on its own.
4. Give it a quick stir, wait ten minutes & give it another quick stir. Don't put the top on the cafetière, just put some clingfilm over the top and put the whole thing in the fridge.
5. Wait 24 hours.
6. Take the whole thing out of the fridge, remove the clingfilm, give it a quick stir, put the top on the cafetière and press down just like you normally would if you were using the thing to make hot coffee.
7. You don't want sludge at the bottom of your cup, so pour it through the drip filter into whatever container you want to store the coffee in (I use a water bottle normally) and keep it in your fridge.

You now have a lovely bottle of the coffee equivalent of blue meth in your fridge. Be warned this mix is strong. I like to drink it in two different ways:

1. Neat in an espresso cup as a replacement for my first espresso of the day.
2. Over lots of ice diluted about 2 parts cold brew to 1 part water if I want a coffee to take with me.

Enjoy!

Short version

1. Make coffee in a cafetière/French press using cold tap water and a fine grind for the beans (not coarse as would be normal)
2. Put it in the fridge to brew for 24 hours
3. Plunge it, then run it through a drip filter