Preheat oven to 160C. Butter a 23cm springform tin with and line the base and sides with baking paper.
Grind the walnuts to a coarse meal in a food processor.
In a large bowl mix together the walnut meal, almond meal, cinnamon, allspice, baking powder and salt.
In another large bowl beat the eggs, butter, orange juice, orange zest, maple syrup and vanilla together until combined and smooth.
Gently fold the two mixtures together, being careful not to over-mix.
Pour the batter into the cake tin.
Bake for 70 minutes or until cooked through and a skewer inserted into the cake comes out clean. Cover the cake with baking paper if it is browning too much during cooking.
To make the spiced syrup gently simmer all of the ingredients in a small saucepan for 5 minutes.
Take the cake out of the oven and allow to cool in the tin. While the cake is cooling pour over the syrup.
Make the crunchy pistachio topping by melting the butter in a small frypan over a low heat. Add the pistachios and maple syrup to the pan and toss altogether for about 5 minutes, until fragrant. Remove from the heat and let come to room temperature.
Once the cake has completely cooled sprinkle over the pistachios.
Serve with creme fraiche, sheeps yoghurt or thick cream.
Replace the maple syrup with honey or rice syrup. Honey will make a sweeter cake, while rice syrup will result in a cake less sweet than maple syrup.