Preheat the oven to 220°C/ fan 200°C / Gas 7.
Wash and dry the potato, pierce several times and place on a baking tray. Bake for 40 minutes until completely soft inside. Set aside and allow to cool for approximately 30 minutes (see notes for a quicker cooking method).
Grease and line a 20x20 brownie tin. Preheat the oven to 200°C/ fan 180°C / Gas 6.
Add the margarine, dark chocolate, maple syrup and vanilla to a saucepan. Melt the mixture over a low heat and stir until silky smooth. Take off the heat and whisk in the almond milk.
In a large mixing bowl sieve the flour, cocoa, baking powder and sugar. Add a good pinch of salt and stir to combine.
Next, return to the sweet potato. Peel and discard the skin. Mash the flesh with a potato masher or fork until it resembles a puree consistency.
Make a well in the dry ingredients and pour in the chocolate mixture. Add in the sweet potato puree along with the chocolate chips. Mix until the ingredients are just combined and no flour is visible.
Spread the mixture into the lined tin. Scatter over a handful of chocolate chips and sprinkle over some sea salt.
Bake for 30 minutes. The brownies should be springy to the touch and a skewer should come out clean with a few moist crumbs. Remove from the oven and allow to cool completely in the tin.