01 - Preheat oven to 350°F. Lightly grease and line an 8-inch square baking pan with parchment paper.
02 - In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and sea salt. Set aside.
03 - In a large bowl, whisk granulated sugar and eggs until the mixture is light in color and slightly thickened, about 2 minutes.
04 - Add vegetable oil and vanilla extract to the sugar and egg mixture, stirring until fully blended.
05 - Fold in the finely grated or puréed beetroot and melted dark chocolate until evenly distributed.
06 - Gently fold the dry ingredient mixture into the wet ingredients until just combined, taking care not to overmix.
07 - Pour the batter into the prepared baking pan and smooth the surface evenly.
08 - Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs attached.
09 - Allow the cake to cool completely in the pan before cutting into 12 squares.