Method

1. Preheat the oven to 175°C, then butter and plain flour in a cake pan.
2. Spread the walnuts on baking paper and toast lightly in the preheated oven for 6 mins. Set them aside on a plate to cool.
3. Grind the nuts in a food processor with the tapioca flour until it becomes very fine. In a medium-sized bowl, combine the ground nuts, remaining flour, baking powder and salt.
4. Set aside 2 tablespoons of honey. In a standing mixer with a paddle attachment, beat the butter with the remaining honey and sugar until light and fluffy for about 3 mins. Scrape down the sides of the bowl.
5. Beat the eggs lightly with the orange zest and vanilla in a small bowl. Add it in thirds to  the butter mixture. Beat well to incorporate after each addition. Scrape down the sides of the bowl. Add the dry ingredients and mix until fully incorporated.
6. Spread the batter evenly in the prepared cake pan. Bake for 35 – 40 mins or until a toothpick inserted in its centre comes out cleanly.
7. Toast about 10 walnut halves on a sheet pan for 8 mins while the cake is baking. Add them to a bowl while still warm and stir in the honey until the walnuts are coated thoroughly with it. Reserve the walnut halves at room temperature to garnish the cake when it is finished.
8. Cool the cake in the pan for 5 mins and then turn out onto a cake rack to cool. Garnish the edge of the cake with the walnut halves before slicing it into wedges.