Grease the shiny side of a double thickness 30 cm/12 in
square of foil with butter. Sift the flour and salt into a bowl. Add
the suet and mix lightly. Stir in the egg and enough milk to form a
soft but not sticky dough. Knead gently on a lightly floured surface.
Roll out to a rectangle about 20 x 25 cm/8 x 10 in.
Spread the jam over, leaving a narrow border about 1 cm/1/2 in all
round. Brush the border with a little milk. Roll up, starting at a
short end. Place on the buttered foil and wrap loosely to allow for
expansion. Make sure the edges are sealed well to prevent moisture
getting into the parcel. Steam for 1 1/2 hours. Unwrap, transfer to a
warmed serving dish, dust with icing sugar and serve with a hot jam
sauce and custard.