Preheat the oven to 200C/180C fan/Gas 6. Grease and line a three-litre cake tin or high-sided baking dish.
Pop the dates and grated parsnip into a mixing bowl, along with the grated, crystallised and ground ginger and bicarbonate of soda. Pour the boiling ginger ale over. Leave for 20 minutes to soften and cool.
In a large mixing bowl, combine the butter, sugar and vanilla with a wooden spoon. Add the eggs, one at a time, mixing well after each addition. Mix in the parsnip and ginger mixture, then fold in the flour and salt until just combined.
Spoon this into the cake tin. Arrange the parsnip slices over the top. Bake for about one hour, or until a skewer inserted into the centre comes out clean. If the top colours too quickly, cover with foil for the last 15 minutes or so. Leave to cool in the tin on a wire rack.
Combine all the sauce ingredients in a pan over a medium heat. Stir often until it comes to the boil. Reduce the heat and simmer for a few minutes until it thickens and the colour turns from blonde to “bronde”.
Spoon the pudding into bowls, then pour over a ladleful of warm sauce and serve with cream or ice cream.