Spread the bread with butter and blackberry jam. Sandwich them and cut into 4 triangles. Place in a greased ovenproof baking dish.
Beat creme fraiche with eggs, caster sugar and orange zest until thick. Gradually add milk, then pour on top of bread.
Lay a damp tea towel in the bottom of a roasting tin. Place the baking dish in the roasting tin on top of the towel. Fill the roasting tin with boiling water from the kettle till it reaches halfway up the sides of the baking dish. Bake the pudding in the preheated oven for 45 minutes or until set.
For the blackberry sauce: Mix jam and orange juice. Heat in a saucepan, but do not boil. Pour over the pudding to serve.