To make the dough, blend the yeast with
the sugar and milk and leave in a warm place for about 20 minutes
until frothy. Place the flour and salt in a bowl and make a well in
the centre. Add the yeast mixture, the egg and oil and work together
to a firm dough. Knead well until elastic and no longer sticky. Place
in an oiled bowl, cover with clingfilm (plastic wrap) and leave to
rise for about 1 hour until doubled in size.
To make the filling, heat the oil and fry (saute) the onions until
soft, then remove from the heat and leave to cool slightly. Reserve a
little egg for glazing, then mix in the remainder with all the
remaining filling ingredients and leave to finish cooling.
Roll out the dough on a lightly floured surface to a 30 x 10 cm/12 x 4
in rectangle. Dot half the butter over two-thirds of the dough. Fold
the plain third of the dough to the centre, covering the butter, then
fold the remaining third over the top. Press the side edges together
to seal. Turn the dough a quarter turn, roll out and repeat once more
with the remaining butter. Wrap in oiled clingfilm and chill for 15
minutes. Roll out and fold once more.
Roll out the dough to a 30 x 23 cm/12 x 9 in rectangle and spread with
the filling, almost to the edges. Roll up from the long side like a
Swiss (jelly) roll. Shape into a ring, moisten the ends and press
together. Make cuts around the dough on the outside edge. Place on a
greased baking (cookie) sheet and leave to rise for 20 minutes. Brush
with the reserved egg. Bake in a preheated oven at 200°C/400°F/ gas
mark 6 for 35 minutes until golden.