Some people I know prefer to serve Neeps and Tatties individually and often the Tatties resemble a standard potato mash which just isn't right in my book!
Neeps and Tatties reminds me very much of a Flemish dish named Stoemp which is worth a try as well
Add the diced swede into a saucepan with boiling salted water and cook until soft and tender. Swede can take a while longer than a potato. When the swede is tender, drain through a colander and leave covered with a tea towel for a few minutes to steam
Add the butter to the swede and using a potato masher, break up the swede and incorporate the butter until the swede is fairly smooth
Grate the nutmeg and seasoning as well as the milk to the mashed swede and bring together. You can season more if you wish
The swede can be kept covered in the fridge until needed
For the tatties, pre heat the oven to 180 degrees and add some oil to a roasting tray and place in the oven so the oil is hot
Add the chopped potatoes to a saucepan of cold salted water and bring to the boil for a few minutes. Drain through a colander and leave covered with a tea towel for a few minutes to steam
Carefully add the potatoes to the hot roasting tray, give a quick stir to coat all the pieces and sprinkle over with sea salt
Roast the potatoes for about 40 minutes until done. When cooked remove from the oven
The potatoes can be cooled and stored in the fridge as well
To serve, heat the oven to 180 degrees. Mix the swede and potatoes together in an oven proof dish, dot with butter and place uncovered to heat through for 20 minutes