Preheat the oven to 325°F and grease and line a 6-inch cake pan.
First, make the frosting: Drain and rinse the cashews and blend in a food processor or high-speed blender with the agave, orange juice and zest, orange extract, coconut oil, and 2 tablespoons of the water. Scrape down the sides frequently until it becomes completely smooth, adding a little more water if necessary. The frosting will go through several stages; nutty, coarse, and eventually silky smooth. You really do have to persevere to achieve the perfect frosting consistency, but don’t take a shortcut by adding too much liquid. Keep blending and it will eventually become a shadow of its former cashew self. Refrigerate until needed.
Mix the polenta, ground almonds, chickpea flour, and baking soda together in a large bowl. Stir through the blood orange zest to ensure it is evenly distributed.
In a separate bowl, vigorously whisk together the oil, blood orange juice, agave, orange extract, and yogurt.
Make a well in the center of the flour and pour in the orange and olive oil mixture. Fold gently and transfer to the prepared cake pan.
Bake for 30 to 35 minutes. Check whether the cake is cooked by inserting a skewer to see if it comes out clean.
Once baked, let cool briefly on a wire rack before removing it from the pan. Set aside until completely cool.
Slather with the chilled cashew frosting, smoothing it around the sides with a spatula. Finally, decorate with crushed pistachios. The cake is best eaten fresh, but will keep for up to 3 days.