In the morning - preheat the oven to 220C/gas 7/fan
200C and bake the potatoes for about
1 hour until the insides are soft.
Whisk the egg yolks, cream, 3 tbsp
horseradish and 1 tbsp lemon juice in
a large bowl. Cut the potatoes in half
and spoon the insides into the bowl,
reserving the skins.
Mash the potato and flavourings together,
then season with salt and a little pepper.
Taste and add more horseradish and/or
lemon juice if required. Pile the potato back
into the skins, then place the potatoes on a
baking tray. Loosely cover with cling film
and keep them cool, not chilled.
Half an hour before serving - dot the filling with scraps of butter and
bake in the oven with the pie for 25-30
minutes until the tops are browned.