Pre heat oven to 180*C. Lightly grease with butter an oven proof rectangle dish (I use glass pyrex).
Sift flour and salt into a bowl, add cold butter mixing with fingers to a coarse crumb like mixture. Add most of the milk into the flour and stir with a knife adding more milk as needed to make a dough. Push dough together with your hands to make a rough ball.
Onto a floured board place the dough and spread into a rough rectangle shape. Sprinkle with a little flour and use a rolling pin to get into a better shape, but it doesn't need to be perfect, about 1 centimetre thick or what looks good.
Spread with jam of your choice until all surface is covered except for that little bit at the end of roll, as it needs to be brushed with milk to seal.
Roll up into a log brushing off any excess flour as you go so it doesn't go into the jam. Brush that end strip with milk and roll to make the join on the underside. Place in baking dish.
For the sauce measure the boiling water then stir in the margarine and sugar until dissolved (if you need more heat pop in the microwave for a few seconds)
Pour the sauce over the jam roll and bake for approx 25 minutes or until cooked. (I like to take out at the 15 or 20 minute mark and spoon some of that sauce over the log to glaze it and pop back in the oven until done)
Take out of the oven and let cool for 5 minutes and slice to serve with custard or ice cream.
This dessert can be served hot or cold.
This uncooked jam roll can be cut into 4 and baked in individual dishes for single serves.
The dough needs to be covered in jam making sure not to over do so that it seeps out the end when baking.
I don't always use all the sauce when serving but I make those measurements anyway.