Let the potatoes steam in the colander for at least 10 minutes after when you drain them. Use a potato ricer, rather than a masher, use more butter than you think can possibly be good for you and refer to the recipe in Gourmet Ireland by Paul Rankin, which is the one I use and which causes grown men to weep with gratitude.
If you want to be more health conscious - follow the initial idea to use a potato ricer but instead of butter, use 2% Greek Yoghurt - it works just as well. Also use a floury potato variety such as Desiree or Maris Piper - but avoid King Edwards - they have the right texture but have a slightly sweet taste which isn't great with something savoury like Champ.
oh goody a question on champ--forget paul rankin et all==boil yer spuds(floury best) finely cut up yer scallions(spring onions) -if you wish heat them in a seperete saucepan with a small amount of milk-then drain (both spuds and scallions -then mash all together(salt to taste).The real art is in the serving-none of those wee tiddly offerings you see on them cookery programmes-put a mountain of it on a plate make a well in the middle and put a big chunk of butter therein---do not decorate with a sprig of parsley lol-(i add hp too) no need for a glass of wine either-glass of cold milk--or best of all cold buttermilk