Preheat your oven to 350°F (175°C). Line a 9x9 inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a large mixing bowl, whisk together the buckwheat flour, cocoa powder, and salt until well combined.
In another bowl, melt the unsalted butter or coconut oil in the microwave or on the stovetop. Allow it to cool slightly before adding it to the mixture.
Add the granulated sugar, vanilla extract, and peppermint extract to the melted butter or coconut oil. Mix until well combined.
Add the eggs one at a time to the wet mixture, whisking well after each addition. This will help create a smooth batter.
Gently fold the dry ingredients into the wet mixture using a rubber spatula. Be careful not to overmix; you want the batter to be just combined.
Fold in the semi-sweet chocolate chips or any other add-ins that you prefer, such as nuts or dried fruit.
Pour the brownie batter into the prepared baking pan and spread it evenly. Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for about 10 minutes. Use the parchment overhang to lift them out of the pan and onto a wire rack to cool completely. Cut into squares and enjoy!
