Heat oven to 180C/160C fan/gas 4.
Butter a sheet of baking parchment. Mix
the flour with the sugar, suet and a good
pinch of salt, then bind with the milk to
make a soft, but not sticky, dough. Add
a dash more milk if it helps to bind the
last few bits left in the bowl.
Roll out the dough on a floured surface
to a 20 x 30cm oblong. Spread with the
jam and scatter with the chocolate,
leaving a border all the way around.
Roll up the dough from one short end
so you have a sausage shape, then gently
pinch the ends to seal in the jam. Carefully
lift onto the prepared parchment.
Fold the paper up over the ends of
the roly-poly, then wrap up quite tightly.
Secure with staples or bulldog clips all
the way along the roll, as this will help
you achieve the classic round shape.
Bake for 50 mins until the roll feels firm
and looks golden through the paper.
Allow to stand for 5 mins before cutting,
as this will stop the jam flowing out.
Drizzle with the melted chocolate and
serve with a jug of warmed custard.