Preheat oven to 350º F. Brush the pan generously with cake release (homemade or store-bought). Place the greased pan on a baking sheet and set aside.
Melt the butter in a small saucepan, whisk in the water and cocoa and heat gently, without boiling. When smooth, remove from heat and let cool slightly.
Add the beets and Creme de Cassis de Dijon to a food processor or mixer and puree until smooth.
Beat together the eggs, buttermilk, vinegar and pureed beet until frothy. Beat in the butter mixture.
Sift together the flour, cornstarch and baking powder, then stir into the mixture with the superfine sugar.
Pour batter into Bundt mold and bake at 350ºF for 55-60 minutes, or until risen and firm to the touch.
Place on a wire rack to cool for 10-15 minutes, then turn out onto wire rack. You may choose to enhance the Creme de Cassis flavour by brushing the still warm cake with the liqueur.
Once completely cooled, decorate with sugar pearls, or sprinkle with icing sugar.