Beat the butter with the sugar until light and fluffy. Add the eggs one at a time beating between each egg. Combine the flour, vanilla sugar, baking powder and salt. Combine the beetroot, beetroot juice and apple cider vinegar then carefully fold the flour mixture and the beetroot mixture alternately into the egg mixture. Pour the batter into a greased springform (approx. 24 cm in diameter). Bake in the middle of the oven for approx. 1 hour at 180°C (conventional oven), then leave to cool on a rack. Carefully slice the cooled cake lengthwise into 2 layers.
Combine the cream cheese, icing sugar, lime zest and juice. Beat the whipping cream until stiff, then fold into the cream cheese mixture. Place one cake layer on a serving dish. Spread 1/3 of the frosting on top. Place the second layer on top. Spread the rest of the icing all over the cake. Start on top, then spread it down sides, creating a smooth surface. To get the icing completely smooth, just dip the palette knife in warm water and dry it off. Draw one large and one small heart on two pieces of paper and cut them out. Use the hollow heart stencils to sprinkle heart shapes on the frosted cake using blueberry dust.
You can substitute beetroot pulp from a juicer for the grated beetroot. The pulp is what is leftover after pressing juice.