Chop the dark chocolate into small pieces and place in a heatproof bowl, along with the butter and the espresso.
Place the bowl over a pot of simmering water, being careful not to let the water touch the bowl, and let it warm through, stirring until the butter and chocolate are both melted, and all ingredients are combined.
Add the Sukrin Gold and the vanilla extract and stir until dissolved. Remove the bowl from the heat and beat in the eggs, one at a time.
Sift the coconut flour, cocoa and baking powder together into a small bowl and then add to the chocolate mixture. Stir briskly until combined with no lumps.
The mixture will look quite runny, but don’t panic. Leave to sit in the bowl for 15 minutes.
Meanwhile, pre-heat the oven to 300° F. Grease and line a standard bundt cake tin and pour the batter in.
Bake for 60 minutes until just set in the center. Remove and allow to cool in the pan before turning out onto a cake rack and serving. Store in the refrigerator for up to 3 days.