Preheat the oven to 350°F.
Soak the dates in warm water for 30 minutes.If they are too dry, soak overnight.
Cook the sweet potato in boiling water, chopped and peeled, for about 20 minutes. Check with a knife if cooked. Strain and mash with a fork.
Spread the sliced almonds on a baking sheet lined with parchment paper and roast for about 8 minutes at 350°F. Leave the oven on to bake the brownie.
Blend the dates. If you have troubles doing so, add a tablespoon or two of the dates water.
Add the mashed sweet potato, brown sugar and melted coconut oil. Blend thoroughly.
In a bowl, mix together the buckwheat flour, cocoa powder and baking powder. Pour in the date/sweet potato and mix until combined with a spatula or wooden spoon. you're going to end up with a pretty thick dough.
Add the chocolate chips and the almonds. I incorporated them by hands, because of the thickness of the dough.
Press the dough in a rectangular dish and bake for 15 minutes at 350°F.