Using an electric mixer, beat the butter with stevia, cinnamon, citric acid and salt until you get a smooth creamy consistency.
Add sour cream, keep mixing and then add baking soda. Continue mixing. Add finely chopped mint, essential oil drops or natural flavouring of your choice and continue with mixing.
At this point add cacao powder and reduce the speed of your mixer. Add the eggs, one by one, and continue mixing on low speed. In the end, add psyllium powder and mix well.
line the baking dish with parchment paper and grease it with some butter. Pour in the brownies. Bake at 180ºC (356ºF) for 15 minutes. (If you like your brownies dry, bake them a bit longer)
When the brownies are baked, cut them in bars or cubes and decorate to your liking*.