Mix the flour, salt, sugar and yeast in a bowl. Add the cream and eggs, mix, knead to form a soft, smooth dough using the dough hook on a food processor. Add the butter and continue to knead for approx. 5 mins. Cover and leave to rise at room temperature for approx. 3 hrs. until doubled in size.
Divide the dough into 12 portions. Remove a walnut-sized piece from each portion and shape into small balls. Shape the remaining portions of dough into larger balls, transfer to the prepared moulds, place the smaller balls on top. Cover and leave to rise for a further 30 mins. Brush the brioches with the egg yolk.
Approx. 20 mins. in the centre of an oven preheated to 180°C. Remove from the oven, allow to cool slightly and serve lukewarm.