Preheat the oven to 200C/400F/gas 6.
Butter a large sheet of baking paper and set aside.
Place the flour, suet, sugar and salt in the large mixing bowl and stir until fully combined.
Slowly stir in the milk to form a soft, spongy dough.
Tip the dough out onto a floured work surface and knead for a few minutes.
Roll the dough out to a 22cm x 32cm rectangle.
Spread the jam onto the dough, leaving a 1.5cm border.
Gently roll the dough up from the short end as you would a Swiss roll.
Place the roll in the centre of the buttered baking paper, seam-side down.
Bring the paper up loosely and join the edges with a fold. Leave at least a 2cm gap between the pudding and the top of the baking paper to allow for expansion when cooking.
Twist the ends of the paper like a Christmas cracker and tie tightly with kitchen string.
Repeat the process with a large piece of kitchen foil so the pudding is wrapped in baking paper on the inside and kitchen foil on the outside.
Place the pudding onto the roasting rack of the roasting tin.
Pour boiling water halfway up the sides of the roasting tin and place in the oven for 40 to 45 minutes.
Remove from the oven and open up the foil and baking paper so the top of the pudding is exposed. Return to the oven for a further 10 minutes or until the top is slightly browned and the dough is fully cooked.
Remove the pudding from the oven and unwrap.
Transfer to a board or serving plate and cut into thick slices. Serve with lots of hot custard or cream.
