I do partial boils of 2.5-3 gallons,regardles of all extract or partial mash. I put 1.5lb out of a 3lb bag of Munton's plain light DME in the boil for the hop additions. Typically one ounce of A hop at 20 minutes,one ounce of B hop at 10 minutes left. Then at flame out,add the remaining 1.5lb of the DME & the Cooper's can,stirring to completely incorporate. Cover & steep for 15 minutes to pasteurize. Since the boiled wort is still at least 180F,& pasteurization happens at about 162F,it'll be fine.
Then chill down to pitch temp in 20 minutes or less,& you'll get little or no chill haze come fridge time.