I love this. My mother used to order this from Marco Polo Hotel for our Christmas dinners so often that I can't fathom Christmas without it.
Do not be tempted to add cheese. The butter and cream produces curds during the cooking process which is essentially cheese so you don't need anymore.
Ingredients
2.5 kg Russet potatoes, peeled
1 fat garlic clove, peeled and minced
1 1/2 teaspoons English mustard powder
675ml single cream
125ml milk
A teaspoon of salt
White pepper
30g unsalted butter
A whole nutmeg
Preheat the oven to 190 C.
Slice the potatoes into 3mm-thick rounds and layer in a buttered deep roasting tin about 20cm by 30cm.
Mix the garlic mince and mustard powder in a jug and pour in the required amounts of cream and milk. Season with salt and white pepper. Taste. The heat of the mustard shouldn't be rasping, but very much present.
Pour this cream over the potatoes, dot with butter and grate over most of the nutmeg. It sounds a lot, but don't worry, it will not overpower.
Bake for about 80 - 90 minutes, till the potatoes are beautifully soft (not al dente) and the gratin's top is blistered in areas. I have one oven and it's not very accommodating, so I usually cook it on the oven floor for an hour while the turkey, stuffing and palmiers cook, shifting it to a higher shelf to continue from there. From here preheat the grill for the vacherin croutons if you are making those.
This tastes best after sitting at room temperature under tin foil for 10 - 15 minutes.
