With DME I have been adding smaller amounts (~1/4 lb) at a time and stirring until dissolved before adding more. This is too slow? Should I add the whole pound or two at once?
Quick is better for dry. It will foam up every time you add some so it's better to just have it do it once than multiple times. Dont worry about it clumping up, it will dissolve as you stir it and as it cooks.
Some people are even proponents of adding all of the extract after the boil. The 60 minute boil is for hops utilization - not to ensure the extract is 'more' dissolved. The yeast will find the sugar.