Hi again SpaceMonkey,
My personal recommendation for a kit based milk stout would go along these lines: Add between 250g and 500g of lactose to a good stout kit. This is in addition to a good fermentable, e.g.; 1 Kg of dark LME. Better still if you could lay your hands on 1 Kg of Muntons Dark malt powder (the Muntons DME has a lovely malty sweetness - hmmmmmm, tasty) and add the 500g of lactose - you will have a beautiful sweet stout regardless of the brand of the stout kit.
These numbers are for a 23 L batch. Halve them if you are using a Malt Shovel Fermenter.
Thanks Keith, guess the malto will be the go although I quite like the idea of a slightly sweeter stout.... how do you think a 50/50 matodextrin/lactose addition would go?
Going the 50/50 isn't what I would do. This is because lactose is an unfermentable sugar; it gets left behind after the fermentation is complete. This not only provides the sweet taste but also gives the beer more body. So lactose does both jobs, adds sweetness and adds body.
If you want body without changing the taste the maltodextrin is the one to use.
Bear in mind that it's the experimentalist in me giving this advice. Changing only one parameter at a time makes interpretation of the results far easier. If you add both the maltodextrin and lactose you will get a very drinkable beer (very, very drinkable), you just wont have as good a feel for the effect of adding only the maltodextrin or only the lactose.
But please, SpaceMonkey, do it the way you want to you, because you will be the one who has the pleasure of drinking the beer.
All the best,
Keith