Put peeled potatoes in a pan of cold, salted water and bring to a boil. Simmer until tender – about 30 minutes.

Meanwhile, in a pan, cook leeks with 6 tablespoons of butter on low heat until very tender. Do not brown the leeks. Add salt and pepper and an optional 1 tablespoon fresh thyme leaves. Thyme goes really well with turkey and gravy! Add in the milk and cream (and optional cream cheese) and bring back just to the boiling point.

Drain potatoes and return to empty pot. Add the milk and leek mixture and mash to your desired consistency.

Spread the mixture in a large shallow baking dish. Cover with tin foil and put into fridge for one day.

To serve:
Preheat oven to 350f
Dot potatoes with remaining butter and bake, covered, in preheated oven until butter is melted and potatoes are warmed through. If your dish isn’t deep it should just take about 20 minutes.