01 - Preheat the oven to 350°F. Grease and line an 8-inch square baking pan with parchment paper.
02 - Whisk together flour, cocoa powder, baking powder, baking soda, and salt in a medium bowl. Set aside.
03 - In a large bowl, whisk granulated sugar and eggs until light and slightly thickened, approximately 2 minutes.
04 - Add vegetable oil and vanilla extract to the sugar and egg mixture and mix until homogeneous.
05 - Fold in the grated or puréed beetroot and melted dark chocolate until fully integrated.
06 - Gently fold the dry mixture into the wet ingredients until just combined; avoid overmixing.
07 - Pour the batter into the prepared pan and smooth the surface evenly.
08 - Bake the batter for 30 to 35 minutes, or until a toothpick inserted in the center yields a few moist crumbs.
09 - Allow the cake to cool completely in the pan before cutting into 12 squares.