Preheat your oven to 325°F (convection) or 350°F (conventional) and line an 8x8-inch (or 9x9) baking pan with parchment paper, leaving an overhang on two sides for easy lifting.
In a mixing bowl, whisk together the buckwheat flour, soft whole wheat flour, sea salt, cacoa powder, and baking powder. Set this dry mixture aside.
In a separate bowl, combine the olive oil, turbinado sugar, and coconut sugar. Mix well until the sugars are fully somewhat dissolved.
Add eggs, one at a time and mix until smooth.
Add vanilla and coffee if using and mix to incorporate.
Gradually add the dry mixture to the wet ingredients, stirring until just combined. Be careful not to over-mix; you want the batter to be smooth and well blended.
Gently fold in the dark chocolate chips using a rubber scrapper, ensuring they are evenly distributed throughout the batter.
Pour the brownie batter into the prepared baking pan, spreading it evenly.
Bake in the preheated oven for approximately 15 minutes (convection) or 18-20 minutes (conventional) or until a toothpick inserted into the center comes out somewhat clean. Be sure not to over-bake; you want them to be slightly fudge-like.
Remove the brownies from the oven and allow them to cool in the pan for a bit.
Use the parchment paper overhangs to lift the brownies out of the pan. Place them on a wire rack to cool completely.
Once cool, cut into small squares.