In another small bowl, mix together all the ingredients for the cinnamon swirl. Pour half the cake batter into a large microwavable mug, or split between two smaller mugs if making two.
Pour the mixture into a microwave-safe mug. • Make sure there is enough space for the cake to rise without spilling over the top! • Put the chocolate spread into the middle of the mix.
Now, interestingly, mug cakes are about the only thing that seems ... so it's a bit more bouncy and it's good." Finally, mix in two tablespoons of dark sugar, though Jamie mentioned any sugar ...