Preheat your oven to 350°F (175°C). Grease an 8×8 inch baking pan with butter or line it with parchment paper, leaving an overhang on the sides for easy removal. If you haven’t already, puree your cooked beets in a food processor until completely smooth. Ensure there are no large chunks remaining, as you want the beets to blend seamlessly into the batter.

Combine the chopped dark chocolate and the melted butter in a heat-proof bowl. Use a microwave in 30-second intervals or a double boiler to melt them together. Stir frequently until the mixture is glossy and smooth. Set this aside for a few minutes to cool slightly so it does not scramble the eggs in the next step.

In a large mixing bowl, whisk the eggs and sugar together until the mixture is pale and slightly frothy. Whisk in the vanilla extract and the cooled chocolate-butter mixture. Once combined, fold in the beetroot puree. The batter will take on a deep, rich mahogany color at this stage.

Sift the all-purpose flour, cocoa powder, and salt directly into the wet ingredients. Using a spatula, gently fold the dry ingredients into the wet mixture. Stop mixing as soon as you see no more streaks of flour. Overmixing will lead to a cake-like texture rather than the desired fudgy consistency. If you are using extra chocolate chips, fold them in now.

Pour the batter into your prepared baking pan and smooth the top with a spatula. Bake for 30 to 35 minutes. Test for doneness by inserting a toothpick into the center; it should come out with a few moist crumbs attached, but not wet batter. Remove from the oven and let the brownies cool completely in the pan before slicing. This cooling period is crucial for the “velvet” texture to set properly.