If you are using a chocolate bar, break it into small bits and combine the chocolate with the butter in a heat-safe bowl. If you bought chocolate chips, simply toss them in the bowl.
Leave the bowl in the microwave for 20 seconds just enough to melt them both. Take out from the microwave and fold continuously with a spoon. Repeat for several times until a uniform, smooth mixture is produced.
Crack the eggs in a separate bowl and mix this with the melted chocolate and butter. Add the vanilla and sweetener for a more flavorful taste. Mix in with the coconut flour and baking powder. Take note of the precise amount of baking powder that should be added so the brownies will not rise too much.
Throw in the chopped walnuts or any other nuts you prefer.
Brush a baking pan with melted butter and pour the mixture in. Optionally, use an oven-safe bowl if there are no baking pans available. Preheat your oven to 350°F before baking the batter for around 25 minutes.
Let the brownies sit for a while after taking them out of the oven. Leave for 20 minutes to cool. To unmold, insert a knife at the edge of your container and run it around carefully to scrape out the brownie.