1
Preheat the oven to 200°C. Line a tray with rock salt, sit the potatoes on it and bake 50 minutes-1 hour until crisp-skinned and soft inside. Rice the pulp; crisp the skins in the oven 8-10 minutes then blend to a fine powder.
2
Make the dough: mix the flour, warm potato mash, yeast, salt and sugar in a mixer with a dough hook for 1 minute.
3
Warm the milk to just above hand temperature and add with 50g crème fraîche and the potato skin powder. Mix 2 minutes, add the eggs and mix 5-6 minutes to a smooth dough.
4
Gradually add the soft butter and mix 10 minutes until glossy. Transfer to a greased bowl, cover and prove until doubled (about 1 hour 15 minutes).
5
Knock back and flatten into a greased cast-iron or baking tray. Cover and prove again until doubled.
6
Season the 100g crème fraîche with salt and lemon juice. Push holes into the dough and stuff with the seasoned crème fraîche and butter.
7
Bake at 200°C for 20 minutes until golden and risen. Brush with butter and garnish with chopped chives.