Mix together the ground flaxseed and water in a small bowl to make a flax egg; set aside to go gloopy.
Place the vegan butter/dairy free margarine, light brown soft sugar and maple syrup in a large pan over a low heat and stir until melted.
Mix in the soy milk, vanilla extract and the flax egg then sift in the flour, cocoa powder and bicarbonate of soda and whisk until no lumps of flour remain.
Place the baking parchment on top of the pudding basin with the fold in the middle, followed by the tin foil. Press the foil over the edge of the pudding basin.
While the pudding is steaming make the sauce. Place the chopped chocolate, soy milk, golden syrup and vanilla extract in a pan over a low heat and whisk gently until melted and smooth. Set aside and re-heat as needed.
Once the pudding is done, cut off the string and remove the tin foil and parchment. Place a serving platter on top and flip over. The pudding should drop out of the basin (you might need to give it a bit of a wiggle). If it is stuck fast, run a knife around the edge to loosen.
Serve right away topped with the chocolate sauce and some ice cream or custard.