1. Preheat your oven to 175°C and line an 20cm by 20cm baking pan with parchment paper.
2. In a medium-sized bowl, whisk together the almond flour, cocoa powder, erythritol, salt, and baking powder until well combined.
3. In a separate bowl, whisk together the melted butter, eggs, and vanilla extract until smooth.
4. Pour the wet ingredients into the dry ingredients and stir until a thick batter forms. If desired, fold in chopped walnuts or sugar-free chocolate chips.
5. Transfer the batter into the prepared baking pan and spread it evenly.
6. Bake in the preheated oven for about 20-25 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.
7. Remove from the oven and let the brownies cool completely in the pan before cutting into squares.
8. Serve and enjoy your delicious keto brownies!