Preheat the oven to 325 degrees. Line a 9-inch square cake pan with parchment paper.
To make the cake, cream the eggs and sugar together in a large mixing bowl. Add the vanilla paste and spices, followed by the honey and butter, and mix until evenly combined. Slowly incorporate the flour until you have a smooth batter. Finally, add the parsnips, walnut pieces and raisins (if using) and mix well again.
Pour the batter into the cake pan and bake for 1 1/4 hours or until deep golden grown on top. Once done, remove from the oven and allow the cake to cool completely.
To make the whipped yogurt, combine the ingredients in a mixing bowl and whip with an electric whisk for a couple of minutes or until the mixture has a consistency you like. Serve the cake with a generous dollop of the whipped yogurt on the side.