Didn'i see this in another forum on here? Anyway,he's talking about steeping the hops,as if there were no plain (un-hopped) malts involved. But since you have 1.5kg of amber DME,you can use about half of that in a 2.5-3 gallon boil to do hop additions in the usual way. 60 minute bittering addition,then,say,20 & 10 minutes for flavor additions. Dry hopping is way better for aroma additions. Do not boil the Cooper's can!
Add the remaining DME & the Cooper's can at the end of the boil,or at flsme out as I do. Stir till completely mixed,cover & steep for 15 minutes to pasteurize. Then proceed as normal.