The coopers stout cans are great. I think they are consistently the best of the coopers products. Get yourself a can of the stout, get 250 gms crushed roast and 80 gms crushed choc grains, stick it in 3 Litres of water and get it to 65 degrees c for about 30 mins. If you can't be bothered doing that then just mix them in with the 3 L of water 24 hours before you brew and let it just sit overnight...it is the flavour and "essence" you want, not trying to extract fermentables out of them. Grab 20gms of Fuggles hop pellets while you're at the homebrew shop getting the grains. Doesn't matter if they don't have any, its just a suggestion.
Bring a couple of litres of water to the boil in a large pot, strain your grain water into it and bring to the boil, add your can of extract and mix it so it is combined nicely with the hot water. Add 1 kg of light dry malt extract. Bring it to the boil and shut it down. CHuck in the hops if you found some (don't stress if you skip this).
As it is a stout and going to be as black as ______________ (fill in your own analogy), don't worry about chilling it (chill haze etc) , just pour the 5L into your lovely, clean, sanitised fermenter, top up to 21 Litres if you like aggressive stouts or 23 Litres if you have nothing to prove.
Use two packs of a slightly fancy dried yeast (in my opinion the coopers yeast ferments very well but tastes fairly average [to me it tastes like pizza dough])...your homebrew shop can give you an idea which ale yeast to use, or if you want to have a go at something new then brew it with Wyeast 1084. If you are a bit of a beer snob or have a sensitive palate then the difference that the 1084 will make will blow your mind.
All respect to previous posters, but if you can't taste the difference between this recipe and a simple addition of 1kg sugar and the kit yeast then I would suggest that homebrewing is not a hobby so much as a way to simply make inexpensive alcohol (and there is nothing wrong with that - I merely mention it as it is a matter of personal preference and volition).
Have fun...always remember that it is what YOU think of the brew at the end of the day that matters. :icon_cheers: