Simple Mashed Potatoes - this one's a keeper

I've been experimenting with mashed potatoes for some time now. I think the method I used today is a keeper. Hence documenting it.

It's an adapted version of http://www.chefsteps.com/activities/pomme-puree. The critical bit is the milk bath. Mine has less butter. Also I don't use all the fluid - I only use just enough to get a smooth mash so the consistency is somewhere between traditional mash and a pure purée.

Result is very smooth, very velvety mashed potatoes, with a lingering savory finish.

This method used 4-5 medium potatoes.

1. Peel and slice potatoes into approx 1-1.5cm slices.
2. Pour milk into a pot (3/4 litre). Basically you'll be using the milk to cook the potatoes so as much milk as will cover the slices.
3. Put a large chunk of unsalted butter (maybe 100g) into the milk with a large pinch of nutmeg powder.
4. Over a fire, heat the milk mixture till a temp of about 80C (careful temp may continue to rise for a bit if you've been using a strong gas fire). Put in the potato slices.
5. Get the temp back up to about 90C and keep it there for 90 mins. I dialed up my oven to 90C using a thermometer to monitor it and put in the pot.
6. The potatoes will not fall apart as long as you keep it at 85-90C. They'll just grow progressively more tender.
7. Drain the mixture and set aside the liquid. Salt the potatoes.
8. Using a sturdy coarse metal sieve, start pushing the potatoes through the sieve. At intervals, ladle some of the cooking fluid over.
9. Once done, taste the potatoes and add more salt if necessary. Mix well.
10. Add a good dollop of Djion Mustard (a tablespoon or two) to taste. Mix well.
11. If the potatoes look too dry at any point, ladle more of the cooking fluid.
12. Taste, taste, taste.
13. If not serving the mashed potatoes immediately, reserve some of the cooking fluid. When  reheating later, spoon over some fluid before reheating.