Preheat the oven to 350F (170C). Line an 8x8-inch (20x20cm) pan with parchment paper.
Make a bain-marie/double-boiler by fitting a glass, ceramic, or metal bowl over a saucepan and adding some water (2 inches/5cm). Do not let the bottom of the bowl touch the water and make sure that the fit is loose enough for the steam to escape. Place the saucepan onto a stovetop and bring the water to a simmer.
Add the chocolate and butter into a bowl and place it over the saucepan. Stir occasionally with a rubber spatula until the ingredients have melted completely. Remove from the heat.
Add the sweetener to the chocolate mixture and mix well until fully incorporated.
Crack the eggs into a small mixing bowl and beat with a fork. Then add the eggs into the chocolate mixture while whisking with a whisk or a hand mixer until fully combined.
Add the vanilla extract and heavy cream and whisk again until combined.
Sift the cocoa powder, coconut flour, and salt through a sieve into the bowl with the wet ingredients and mix using a spatula until no dry ingredients are left. Fold in some extra chocolate bits if desired.
Pour the brownie mixture into the prepared pan and smooth out the surface. Sprinkle with some extra chocolate bits and bake for 20-25 minutes, until the toothpick inserted into the center comes out a little bit wet and with a few brownie crumbs on it.
Remove from the oven and let it cool down completely before slicing and serving.