01 - Preheat 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 - Incorporate vegetable oil and vanilla extract into the egg mixture, stirring until well combined.
05 - Fold grated or puréed beetroot and melted dark chocolate into the wet ingredients until evenly distributed.
06 - Gently fold dry ingredients into the wet mixture until just combined; avoid overmixing to maintain moisture.
07 - Pour batter into the prepared pan, smoothing the surface evenly.
08 - Bake for 30 to 35 minutes until a toothpick inserted in the center comes out with a few moist crumbs.
09 - Allow cake to cool completely in the pan before cutting into 12 squares.