I have found that if you put the potato in cool water and then put the stove on medium to medium low heat covered, the potato cooks more evenly.
This is a common mistake made by folks
The common russet potato is not the best for mashing in my opinion but, ‘to each their own on that one.
Some chiefs recommend a mix of two different kinds of potatoes for mashing.
It is very easy to over cook the potato when it comes to mashing them and it is best to let them steam off to get rid of the excess moisture in them before mashing.
And I think some folks us too much milk in the mix, I don’t use hardly any.
Just more sinful butter, don’t tell my wife as I hide this from her.
And last but not least here is a link on potatoes that may help.
I didn’t mean for this to turn into a cooking class I’m just trying to help.
http://en.wikipedia.org/wiki/Red_Gold_potato
I like Yukon gold’s and red potatoes for mashing.
Worth