Preheat oven to 180°C/350°F/Gas 4
Grease 2 x 20cm sandwich tins and line the bases with parchment paper.
Sieve the flour and baking powder together, cream the butter with the sugar until light and fluffy. Add the eggs one at a time, adding a tablespoon of the flour with each egg. Fold in the sieved flour, mixed spice, grated Piccolo parsnip, pecan nuts, vanilla, maple syrup, rind of the orange and 1 tablespoon of orange juice. If the mixture is still too stiff add a little milk, it should be a dropping consistency. Spoon the mixture into the cake tins and bake in the oven for 25-30 minutes until the top just springs back when lightly pressed. Cool the cake slightly in the tins before turning out onto wire racks.
To make the frosting, place the mascarpone and cream cheese in a bowl and beat until soft, stir in the maple syrup, orange rind and a little juice to give a spreadable, but thick consistency.
When the cake is cool spread half of the frosting over one half of the cake and sandwich the two halves together. Then spread the rest of the frosting on top of the cake and decorate with pecan nut halves. Dust with icing sugar.